Szeto Schiller 31 is the long-hand name for SS-31, and it is how a surprising number of people first type it into a search box. They have heard Szeto Schiller 31 mentioned in a talk or seen it in a slide, caught the two surnames and the number, and gone looking. If that is how you got here, welcome. You are in the right place.

This article is about how Szeto Schiller 31 has actually been studied. Not the mechanism, which we cover elsewhere, and not the clinical trials. The models. Which cells, which tissues, which kinds of stress, and what was measured. If you are planning your own work with Szeto Schiller 31, seeing what others did, and what they wished they had done differently, is the fastest way to a sound design.

We supply Szeto Schiller 31 for research and have talked through a great many study plans with customers. What follows draws on the published literature and on those conversations.

A quick word on what Szeto Schiller 31 is

Szeto Schiller 31 is a synthetic peptide of four amino acids, D-Arg-Dmt-Lys-Phe-NH2, made by Hazel Szeto and Peter Schiller in the early 2000s. It enters cells without help, concentrates at the inner mitochondrial membrane and binds a lipid called cardiolipin. It is also known as elamipretide and MTP-131.

If any of that is new, three of our other articles fill in the background: the Szeto-Schiller peptide family, MTP131 and cardiolipin, and the essential facts about SS-31.

One principle runs through every model below and is worth stating now. Szeto Schiller 31 does very little to healthy mitochondria. Its effects show up when mitochondria are stressed, damaged or old. A study in unstressed cells is likely to find nothing, and that null result will not mean much.

Model 1: Isolated mitochondria

The simplest system. Mitochondria are purified from tissue, usually liver, heart or kidney, and studied in a buffer.

This is where the earliest work was done. Researchers showed that Szeto Schiller 31 was taken up by isolated mitochondria, that it reduced the production of hydrogen peroxide, and that it prevented the swelling and membrane rupture that calcium overload causes.

Typical measurements:

• Oxygen consumption, with different fuels to isolate each respiratory complex.
• ATP production rate.
• Hydrogen peroxide release.
• Swelling, followed by light scattering.
• Cytochrome c release.

What this model is good for: clean mechanistic questions with no interference from the rest of the cell. What it is bad for: anything that takes longer than an hour or two, because isolated mitochondria do not last.

A practical note. The isolation procedure itself damages mitochondria to some degree, and how much depends on the hands doing it. That damage is, in a sense, the stress Szeto Schiller 31 acts on. Results can vary between labs for this reason. Keep your preparation consistent and report its quality.

Model 2: Cultured cells under oxidative stress

One step up. Cells grown in a dish are exposed to something that generates reactive oxygen species, and Szeto Schiller 31 is added before, during or after.

Common stressors include hydrogen peroxide, tert-butyl hydroperoxide, high glucose, and inhibitors of the electron transport chain such as antimycin. Cell types have ranged from kidney tubule cells and heart muscle cells to neurons, retinal cells and endothelial cells.

Typical measurements:

• Cell survival.
• Mitochondrial membrane potential, using fluorescent dyes.
• Reactive oxygen species, with probes such as MitoSOX.
• Markers of apoptosis.
• Oxygen consumption on a plate-based analyser.

This is the most accessible model and the one most new users of Szeto Schiller 31 start with. A few things we have seen go wrong.

Too much stress. If the insult kills ninety percent of cells in an hour, nothing will rescue them. Titrate the stressor so that you get partial damage with room to improve.

Too little stress. The opposite problem. Healthy cells, no effect.

Glucose-fed cells. Many cell lines in standard high-glucose medium barely use their mitochondria. They make their ATP by glycolysis. Switching to galactose medium forces them to rely on oxidative phosphorylation, and mitochondrial effects become far easier to see.

Dye artefacts. Some membrane potential dyes are themselves positively charged and compete for the same space. Confirm with a second method.

Model 3: Ischaemia and reperfusion

This is the classic. Blood supply to an organ is interrupted for a set time and then restored. The return of oxygen causes a burst of reactive species and a wave of mitochondrial damage that kills more tissue than the oxygen shortage alone.

Szeto Schiller 31 has been tested in ischaemia-reperfusion models of the heart, kidney, brain, liver and skeletal muscle. The kidney work is especially thorough. In rats, treatment preserved the internal structure of mitochondria in tubule cells, sped up the recovery of ATP, and reduced cell death and later scarring.

Typical measurements:

• Infarct size or area of tissue death.
• Organ function, such as serum creatinine for kidney or ejection fraction for heart.
• Mitochondrial structure by electron microscopy.
• Tissue ATP content.
• Markers of inflammation and fibrosis at later time points.

The lesson from this model is about timing. In animals, Szeto Schiller 31 is usually given shortly before blood flow is restored, under tightly controlled conditions. When the same idea was tried in heart attack patients, where timing cannot be controlled so precisely, the main endpoint was missed. Our article on elamipretide covers that trial. If you work in this model, think carefully about when Szeto Schiller 31 is present relative to reperfusion, and say so clearly in your methods.

A cell culture version exists too: deprive cells of oxygen and glucose for a period, then restore both. It is a reasonable first step before animal work.

Model 4: Ageing

Mitochondrial function declines with age in most tissues. Old mitochondria make less ATP and leak more.

The best-known study of Szeto Schiller 31 in this setting was published in 2013. Old mice were given a single treatment, and mitochondrial energetics in leg muscle were measured in the living animal using magnetic resonance and optical spectroscopy. Within an hour, ATP production and the efficiency of oxygen use had moved back toward the values seen in young mice. Young mice given the same treatment did not change. After a week of daily treatment, the old mice had better resistance to fatigue and ran for longer.

Later work extended this to the ageing heart, where eight weeks of treatment improved the relaxation phase of the heartbeat in old mice, and to ageing kidney and brain.

Typical measurements:

• In vivo ATP production.
• Exercise capacity and fatigue resistance.
• Heart function by ultrasound.
• Protein oxidation and redox state in tissue.

What makes ageing an attractive model is that the stress is natural and no injury has to be inflicted. What makes it hard is cost and time. Old mice are expensive and scarce. If you plan such a study, order animals well ahead and make sure you have enough compound from a single lot to cover the whole thing. Our SS31 buying guide has a section on sizing an order.

Model 5: Heart failure

Failing hearts have abnormal mitochondria, reduced cardiolipin and poor energy reserves.

Szeto Schiller 31 has been tested in mice with heart failure caused by pressure overload or by angiotensin, in rats after heart attack, and in dogs with failure induced by repeated tiny blockages of the coronary arteries. In the dog study, three months of daily treatment improved the heart's pumping function and normalised several measures of mitochondrial respiration in heart tissue.

There is also work on human tissue. Heart muscle taken from failing hearts at the time of transplant was treated in the lab, and mitochondrial oxygen use improved within hours.

Typical measurements:

• Ejection fraction and chamber volumes.
• Blood markers of cardiac stress.
• Mitochondrial respiration in tissue samples.
• Cardiolipin content and composition.
• Assembly of respiratory supercomplexes.

Human trials in heart failure did not reproduce the animal benefit over four weeks. Whether that is a question of duration, dose, patient selection or biology is not settled. For bench researchers it argues for longer treatment periods and for measuring tissue-level changes, not only organ function.

Model 6: Genetic mitochondrial disease

Some of the most informative work has been done in models of inherited disease, because the defect is defined.

Barth syndrome is the clearest example. It is caused by loss of tafazzin, the enzyme that matures cardiolipin. Researchers have used cells from patients, including stem-cell derived heart muscle cells, and mice with reduced tafazzin. In these systems Szeto Schiller 31 improved mitochondrial structure and function despite the underlying lipid defect remaining.

Other models include cells from patients with Friedreich ataxia and with defects in mitochondrial DNA maintenance.

Typical measurements:

• Cristae structure by electron microscopy.
• The ratio of immature to mature cardiolipin.
• Respiration and ATP output.
• Contractile function in heart cells.

If you have access to patient-derived cells, this is where Szeto Schiller 31 can be tested most directly against its proposed target. It is also the area where a pharmaceutical form of Szeto Schiller 31 eventually won approval, in 2025, for Barth syndrome.

Model 7: The eye

The retina uses a great deal of energy, and its cells are packed with mitochondria. Mitochondrial decline is thought to contribute to several eye diseases.

In the lab, Szeto Schiller 31 has been tested on retinal pigment epithelial cells and other retinal cell types under oxidative stress, and in animal models of diabetic eye disease, glaucoma and retinal degeneration. Reported effects include better cell survival, preserved mitochondrial membrane potential and less cell death.

Typical measurements:

• Cell viability.
• Mitochondrial morphology by imaging.
• Visual function tests in animals.
• Retinal thickness and layer structure.

This model is worth knowing about because it is technically approachable. Retinal pigment epithelial cell lines are widely available and easy to grow, and they respond well to mitochondrial stressors.

Controls that make a study convincing

Whichever model you choose, the controls matter more than anything else. A list we would hand to anyone starting out.

• Vehicle. The same solvent with no peptide, handled identically.
• Unstressed plus peptide. To show that Szeto Schiller 31 alone does nothing to healthy cells. This is a feature, not a failure.
• A general antioxidant, such as N-acetylcysteine. If it does not reproduce the effect, simple scavenging is unlikely to be the explanation.
• A different mitochondria-targeted antioxidant, such as MitoQ, where relevant.
• SS-20, if you can obtain it. It reaches mitochondria but cannot scavenge radicals, so it separates location from chemistry.
• More than one concentration. Published cell studies have used a wide range, from nanomolar to micromolar. Run a series and find where your system responds.
• More than one time point.

And one that is easy to forget: confirm Szeto Schiller 31. Keep the Certificate of Analysis, note the lot number in your records, and if you can, run your own HPLC on arrival. Our piece on SS31 peptide purity testing explains how.

Practical points on preparing Szeto Schiller 31

Szeto Schiller 31 dissolves readily in water. Make a concentrated stock in sterile water or buffer, split it into single-use portions, and freeze them. Dilute into medium on the day. Avoid repeated freezing and thawing.

When calculating concentrations, remember that the powder is a salt. Szeto Schiller 31 itself may be 65 to 85 percent of the weight depending on the counter-ion. Ask your supplier which convention their label uses. The arithmetic is worked through in our article on elamipretide peptide chemistry, and the storage routine is in the SS-31 peptide storage guide.

Choosing a grade for your model

Different models make different demands on the material.

• Screening stressors and concentrations in cells: Standard Grade is enough.
• Routine cell culture experiments: High Purity Grade.
• Isolated mitochondria, mechanistic or analytical work that will be published: Ultra-Pure Research Grade or the 50 mg vial.
• Animal studies and anything needing large amounts from one lot: Bulk Research Grade, up to 500 mg per vial.

How to order Szeto Schiller 31 from us

We list it as SS-31. Our minimum order is 50 units with no upper limit, and you can mix grades and sizes or add other compounds such as BPC-157, TB-500, GHK-Cu and Retatrutide.

Open the SS-31 peptide page, press Order beside the size you want, and enter the quantity and your delivery address. Tell us in the message if you need the whole order from a single lot, which we recommend for any study. We reply by email with the total, normally the same day. We accept Apple Pay, Zelle, Chime, Cash App, USDT and Bitcoin. The Certificate of Analysis ships with the order, or ahead of it if you ask through the contact page.

All material is sold for laboratory and in-vitro research only. It is not for human or animal consumption.

A four-week pilot plan

If you are starting from nothing, here is a pilot we have seen work in several labs. It uses cultured cells and needs no special equipment beyond a plate reader. Adjust it to your own system.

Week one. Get your cells growing well in galactose medium. This alone can take a few passages, and some lines do not tolerate it, which is worth knowing early. Reconstitute one vial of Szeto Schiller 31, make single-use aliquots, and freeze them.

Week two. Find your stressor dose. Treat cells with a range of concentrations of your chosen stressor and measure survival a day later. You are looking for the dose that leaves about half to two-thirds of cells alive. Too gentle or too harsh and there is nothing to rescue.

Week three. Run Szeto Schiller 31. Using the stressor dose from week two, add Szeto Schiller 31 across a wide range, say six concentrations spanning three orders of magnitude, with a short pre-treatment. Include vehicle, peptide-only and stressor-only wells. Measure survival and one mitochondrial readout, such as membrane potential.

Week four. Repeat week three exactly, with fresh aliquots, on a different day. If the result holds, you have a working model. If it does not, you have learned that cheaply.

The whole pilot uses a few milligrams of compound. Standard Grade is fine for it. Only once the model is behaving do you need to think about higher grades and larger quantities.

What to report when you write it up

A lot of published work on Szeto Schiller 31 is hard to compare because key details are missing. If you want your study to be useful to others, include these.

• The supplier, grade and lot number of Szeto Schiller 31.
• Its purity and how that was determined.
• Whether stated concentrations refer to the salt or the free peptide.
• The solvent and stock concentration.
• How long before, during or after the stress Szeto Schiller 31 was present.
• The medium, including glucose or galactose and serum content.
• Passage number and source of cells, or age, sex and strain of animals.
• Every control you ran, including the ones that showed nothing.
• How many independent repeats, and what counts as one.

The ones that showed nothing matter. A clear statement that Szeto Schiller 31 had no effect on unstressed cells is a result, and it supports the specificity of whatever effect you did see.

Budgeting compound for each model

How much you need varies enormously between models, and running out mid-study is a common and avoidable problem.

Cell culture uses very little. At micromolar concentrations in a few millilitres of medium, a single 5 mg vial covers dozens of plates.

Isolated mitochondria use more, because concentrations are often higher and preparations are repeated many times. Plan on tens of milligrams for a full study.

Animal work is where the quantity jumps. Daily treatment of a cohort of mice for several weeks can run to hundreds of milligrams. Larger animals need more again. This is where Bulk Research Grade makes sense, and where it is most important to get the whole amount from a single lot of Szeto Schiller 31.

Whatever the model, work out the total before you order, add a third for losses and repeats, and round up. Then tell your supplier you want it from one lot. A study that changes lot halfway is a study with an extra variable, and reviewers will ask about it.

One more thing on negative results

Not every experiment with this compound works, and not every model responds. The clinical record makes that plain. If you run a careful study with proper controls and see no effect, that is worth knowing and worth publishing. The field has more than enough positive reports from small studies. What it lacks is a clear map of where Szeto Schiller 31 does not help, and that map can only be drawn from honest negative results.

Questions about working with Szeto Schiller 31

Which model should a new lab start with?

Cultured cells under a titrated oxidative stress, ideally in galactose medium. It is cheap, quick and tells you whether your system responds.

Why did I see no effect?

The most common reasons are unstressed cells, cells running on glycolysis, too severe an insult, or too short an exposure.

What concentration should I use?

There is no single answer. Published work spans a wide range. Run a concentration series in your own system.

Is Szeto Schiller 31 toxic to cells?

At the concentrations used in the published literature it has generally been well tolerated. Always include a peptide-only control.

Where can I find the published studies?

Search PubMed for SS-31 or elamipretide and filter by the tissue or model you are interested in.

Final thoughts

Seven models, one recurring theme. Szeto Schiller 31 acts on mitochondria that are in trouble and leaves healthy ones alone. Build your study around a real, measurable mitochondrial stress, treat for long enough, measure structure as well as function, and include the controls that let you say why something happened and not merely that it did.

If you would like to talk through a design before ordering, write to us. We cannot run your experiment, but we have seen enough of them to help you avoid the usual mistakes.

A Szeto-Schiller peptide is any member of a small group of synthetic peptides, four amino acids long, that cross cell membranes on their own and collect in mitochondria. There are only a handful of them. One, SS-31, became a medicine. The others are mostly remembered as footnotes, which is a pity, because you cannot really understand SS-31 without knowing where it sits in the family.

We sell SS-31, and the question of what the SS stands for comes up constantly. The answer is two surnames and a good story about paying attention to results you did not expect. Here is the family, member by member, and what each one teaches.

Who Szeto and Schiller are

Hazel Szeto is a physician and pharmacologist who spent most of her career at Weill Cornell Medical College in New York. Her background was in opioids and how drugs reach the brain and the fetus.

Peter Schiller is a peptide chemist who ran a laboratory at the Clinical Research Institute of Montreal for decades. His speciality was designing opioid peptides: small synthetic molecules that act on the same receptors as morphine but with different properties.

They began working together in the 1990s. Schiller's lab made the molecules. Szeto's lab tested what they did in cells and animals. The aim was better painkillers. Nobody involved was thinking about mitochondria.

The idea behind every Szeto-Schiller peptide

Before going through the compounds one by one, it helps to see what they share. Every Szeto-Schiller peptide is built on the same plan.

• Four amino acids.
• Aromatic and positively charged residues in alternation.
• A net charge of plus three at body pH.
• A D-amino acid in the first or second position.
• An amide cap at the far end.

Aromatic residues are oily and like to sit in membranes. Charged residues are the opposite, and normally keep a molecule out of membranes altogether. Alternating the two in such a short chain produces something that can do both: dissolve freely in water and still slip across a lipid barrier.

That was not the textbook expectation. The rule of thumb in drug design was that three positive charges would stop a molecule getting into cells at all. These peptides broke the rule, and working out why is what opened up the whole field.

SS-01: the starting point

The first compound in the line has the sequence Tyr-D-Arg-Phe-Lys-NH2. Schiller's group published it in the late 1980s under the name DALDA. It was designed as a highly selective activator of the mu opioid receptor, the one responsible for most of morphine's painkilling effect.

DALDA was meant to stay out of the brain. With three positive charges it was not expected to cross the blood-brain barrier, which made it interesting as a painkiller that would act only in the body, without sedation or addiction.

In the numbering used later, DALDA became SS-01. It is an opioid first and foremost. It has a tyrosine with a free phenol group, which gives it some ability to react with free radicals, but that was not noticed or cared about at the time.

SS-02: the surprise

The next step was a small change. Replace the tyrosine at position one with 2,6-dimethyltyrosine, abbreviated Dmt. This is a common trick in opioid chemistry. The two extra methyl groups usually increase potency.

The result, Dmt-D-Arg-Phe-Lys-NH2, was an extraordinarily potent painkiller in animals, far stronger than morphine when given into the spinal fluid. It was called [Dmt1]DALDA, and later SS-02.

Then came the unexpected findings. Szeto's lab found that this highly charged peptide was taken up by cells. Not slowly, and not by any transporter they could identify. It simply went in. When they looked at where it went inside the cell, it was in the mitochondria, concentrated hundreds to thousands of times over.

A second finding followed. Dmt is a much better radical scavenger than plain tyrosine. So here was a molecule that delivered an antioxidant group directly to the place in the cell where most reactive oxygen species are made.

That was interesting in its own right. But SS-02 was still a powerful opioid. You could not study its mitochondrial effects in an animal without also sedating the animal. The opioid activity had to go.

SS-31: the same parts, rearranged

Opioid peptides need their tyrosine, or Dmt, at the very first position, with a free amine on it. That is how the receptor recognises them. Move it and the opioid activity vanishes.

So that is what they did. Take the same four building blocks and shuffle them: D-Arg-Dmt-Lys-Phe-NH2. The Dmt is now second. The alternating pattern is preserved, the three charges are preserved, the radical-scavenging phenol is preserved. The opioid activity is gone.

This is SS-31. It kept everything that made SS-02 interesting to mitochondria researchers and dropped the one thing that made it unusable. A 2004 paper in the Journal of Biological Chemistry laid out the results: uptake into cells and mitochondria, reduction of reactive oxygen species, prevention of mitochondrial swelling, and protection of heart tissue from injury.

Of every Szeto-Schiller peptide made, this is the one that went furthest. It was licensed to a company, renamed several times, tested in thousands of patients and eventually approved in 2025 for a rare mitochondrial disease. We tell that story in our article on elamipretide, and we cover the naming in MTP-131 and its other names.

SS-20: the control that turned out to be more

The fourth compound was designed to answer a question. Is the benefit of SS-31 down to the antioxidant Dmt group, or to something else about the Szeto-Schiller peptide?

SS-20 has the sequence Phe-D-Arg-Phe-Lys-NH2. No tyrosine, no Dmt, no phenol. It cannot scavenge radicals. It has no opioid activity either. But it has the same alternating pattern and the same charge, and it goes to mitochondria just the same.

The expectation was that SS-20 would do nothing, proving that the antioxidant group was the active part. That is not what happened. In a number of models SS-20 was protective too. It reduced reactive oxygen species even though it could not react with them directly.

This was an important clue. If a Szeto-Schiller peptide with no scavenging ability still reduced oxidative damage, then scavenging could not be the whole mechanism. Something about simply being at the inner mitochondrial membrane was doing the work, perhaps by making the electron transport chain run more cleanly so that fewer reactive species were produced in the first place.

That line of thinking led, a few years later, to the discovery that each Szeto-Schiller peptide bind cardiolipin. We explain that in detail in our piece on MTP131 and cardiolipin.

SS-20 is still used in research as a comparison compound. It was also taken into early development by the same company under a separate code.

The family at a glance

It can be hard to keep them straight, so here they are side by side.

• SS-01, Tyr-D-Arg-Phe-Lys-NH2. Opioid activity: yes. Radical scavenging: weak. Goes to mitochondria: yes.
• SS-02, Dmt-D-Arg-Phe-Lys-NH2. Opioid activity: very strong. Radical scavenging: yes. Goes to mitochondria: yes.
• SS-31, D-Arg-Dmt-Lys-Phe-NH2. Opioid activity: none. Radical scavenging: yes. Goes to mitochondria: yes.
• SS-20, Phe-D-Arg-Phe-Lys-NH2. Opioid activity: none. Radical scavenging: none. Goes to mitochondria: yes.

Read down the last item in each line. Every one of them reaches mitochondria. That property comes from the shared architecture, not from any single residue. The other properties were switched on and off by changing which amino acid sat where.

It is a tidy piece of medicinal chemistry. Four compounds, each differing from the next by one deliberate change, each answering a specific question.

How a Szeto-Schiller peptide gets into mitochondria

This puzzled people for a while, and the full answer is still debated. What is known is this.

Uptake into cells is fast, taking minutes. It does not need energy. It is not blocked by inhibitors of the usual transport routes. It happens at low temperature. All of that points to the Szeto-Schiller peptide passing directly through the membrane and not being carried by a protein.

Once inside, it concentrates at the inner mitochondrial membrane. Compounds like MitoQ get there by being pulled in by the membrane's electrical potential, and they end up in the innermost compartment. The Szeto-Schiller compounds depend much less on that potential. Even when mitochondria are depolarised, a large share of the Szeto-Schiller peptide still gets in and stays bound.

The reason is cardiolipin. The inner membrane is rich in this doubly negative lipid, and a peptide with three positive charges and two aromatic rings has a strong affinity for it. The peptide is not so much pumped in as drawn to a surface it sticks to.

This has a practical upside. Sick mitochondria tend to have low membrane potential. A compound that relies on potential will reach them poorly. A Szeto-Schiller peptide still finds them.

Why only SS-31 is widely sold

If you go looking to buy a Szeto-Schiller peptide for research, you will find SS-31 everywhere and the others almost nowhere. There are simple reasons.

SS-01 and SS-02 are opioids. SS-02 in particular is extremely potent. That brings regulatory complications that most suppliers and most labs would prefer to avoid, and it makes them unsuitable for studying mitochondria in isolation.

SS-20 is useful mainly as a control. Demand is small, so few suppliers keep it in stock. It can be made to order.

SS-31 has the published literature, the clinical history and the clean pharmacology. It is the one researchers ask for. It is the only one we carry as a stock item, in four grades:

• Standard Grade, 98 percent or better.
• High Purity Grade, for everyday cell work.
• Ultra-Pure Research Grade, 99.5 percent or better with HPLC and mass spec.
• Bulk Research Grade, in vials up to 500 mg.

If your study design needs SS-20 alongside it as a control, write to us through the contact page. We will tell you honestly whether we can source it for you and how long it would take.

What the family teaches about experimental design

Even if you only ever use SS-31, the history of the other three is a lesson in controls.

The original researchers did not just show that their compound worked. They made a version without the opioid activity to rule that out. They made a version without the antioxidant group to test whether that was the mechanism. Each new Szeto-Schiller peptide was a question put to the previous one.

You can apply the same thinking at the bench.

• If you see an effect with SS-31, ask whether a general antioxidant such as N-acetylcysteine reproduces it. If not, scavenging is unlikely to be the explanation.
• Ask whether a mitochondria-targeted antioxidant of a different class reproduces it.
• If you can get SS-20, see whether it does the same. If it does, the effect is about membrane localisation and not about Dmt.
• Test in both stressed and unstressed conditions. The peptides do little in healthy mitochondria.

We go further into models and controls in our piece on Szeto Schiller 31 research models.

Handling is the same across the family

Chemically these compounds are close cousins. All are highly water-soluble, all are supplied as freeze-dried salts, all are stable when kept dry and cold. The practical advice for one applies to the rest: store at minus 20, warm the vial before opening, dissolve in water or simple buffer, split into single-use portions.

The routine is laid out in our SS-31 peptide storage guide, and the points about salt forms and net content in elamipretide peptide chemistry apply equally.

Ordering from us

We supply wholesale, from a minimum of 50 units with no upper limit. You can combine SS-31 with our other compounds, BPC-157, GHK-Cu, Retatrutide and TB-500, to reach the minimum.

To order, open the SS-31 peptide page, press Order beside the grade and size you want, and fill in the quantity and delivery address. We reply by email with the total, usually on the same day. We take Apple Pay, Zelle, Chime, Cash App, USDT and Bitcoin, and every order ships with the Certificate of Analysis for its lot.

Everything we sell is for laboratory and in-vitro research only. It is not for human or animal use.

Why four residues, and why this pattern

People sometimes ask whether a Szeto-Schiller peptide could be longer, shorter or arranged differently and still work. The original researchers asked the same thing and tested it.

Four residues seems to be close to the smallest unit that carries the pattern. You need at least two aromatic and two charged groups to alternate, and that takes four positions. Shorter and the pattern is gone.

Longer chains were not pursued in the same way, partly because the short ones already worked and partly because each extra residue makes a peptide harder to get into cells and easier for enzymes to cut.

The order matters in subtle ways. A Szeto-Schiller peptide can start with an aromatic residue, as SS-02 and SS-20 do, or with a charged one, as SS-31 does. Both arrangements reach mitochondria. What changes is everything else: receptor activity, scavenging ability, and probably the fine detail of how the Szeto-Schiller peptide lies on the membrane.

The D-amino acid is there for stability, as is the amide at the end. Without them, the peptides would be broken down in minutes. With them, they last for hours in blood and tissue.

So each Szeto-Schiller peptide is a compromise worked out by trial: as small as possible, as stable as possible, with the charge and oiliness balanced so that it dissolves in water and still crosses membranes. That balance is narrow, which is one reason there are only a few of them.

What came after the original four

The family did not stop growing in 2004. Once the cardiolipin mechanism was understood, the company that licensed the compounds began designing new molecules on the same principle. These later compounds are not all peptides in the strict sense. Some replace parts of the backbone with other chemistry to improve how they are absorbed or how well they reach particular tissues such as the brain.

They carry different code names and are at earlier stages of testing. We mention them only so that you are not confused if you meet them in the literature. They are descendants of the Szeto-Schiller peptide idea, not members of the original set, and they are not available as research chemicals in the way SS-31 is.

Other groups have made their own variations as well, attaching the four-residue motif to dyes for imaging or to other active groups to carry them into mitochondria. In that sense the Szeto-Schiller peptide has become a delivery tool as well as a compound in its own right.

Mix-ups we see with the Szeto-Schiller peptide names

A few recurring confusions, briefly.

SS-31 and SS-20 are not two strengths of the same thing. They are different sequences with different properties.

SS-31 is not thirty-one amino acids long. The number is a serial number. It has four.

The SS does not stand for a chemical term. People have guessed at sulfur-sulfur, as in a disulfide bond, or at some abbreviation for a class of drug. It is just Szeto and Schiller.

A Szeto-Schiller peptide is not the same as a cell-penetrating peptide in the usual sense. Classic cell-penetrating peptides such as TAT are longer, rely on different uptake routes and do not home to mitochondria.

And not every mitochondria-targeted peptide is a Szeto-Schiller peptide. Other research groups have developed separate families with their own designs. The name belongs to this particular series.

Why the history is worth knowing as a buyer

This might all sound academic. It has a practical edge. A supplier who can tell you how SS-31 differs from SS-20, and why one is an opioid relative and the other is not, understands what they are selling. One who cannot is reselling a powder. When you are deciding whom to trust with a study, that is a fair thing to test, and a two-line email will do it.

A quick test of understanding

If you can answer three questions, you have the family straight. Which Szeto-Schiller peptide is an opioid? SS-01 and SS-02. Which Szeto-Schiller peptide cannot scavenge radicals? SS-20. Which one do researchers actually order? SS-31. Everything else in this article is detail hung on those three answers.

Questions about the Szeto-Schiller peptide family

How many Szeto-Schiller peptides are there?

Four are commonly discussed: SS-01, SS-02, SS-20 and SS-31. Others were made and tested but did not become widely used.

Is every Szeto-Schiller peptide an antioxidant?

No. SS-20 has no radical-scavenging group. That is the point of it.

Is SS-31 an opioid?

No. Its relatives SS-01 and SS-02 are, but in SS-31 the residue the opioid receptor needs has been moved out of position. It has no meaningful opioid activity.

Why are the numbers not in order?

They reflect the order in which compounds were made in the lab, and many in between were not pursued.

Where can I read the original research?

A good start is to search PubMed for Szeto-Schiller peptides. Hazel Szeto has written several clear review articles.

Closing thought

The story of the Szeto-Schiller peptide family is a reminder that the most useful result in a project is sometimes the one that does not fit. Two researchers were making opioids. One of their compounds turned up in the wrong part of the cell. They asked why, changed one thing at a time, and ended up founding a new class of mitochondrial compounds.

SS-31 is the member of that class that lasted. If you would like to work with it, our essential facts about SS-31 is the place to start, and the SS31 buying guide will help you choose a grade. A general overview is also on Wikipedia.

MTP131 is usually described in one line: a mitochondria-targeted peptide that binds cardiolipin. True, and almost useless unless you already know what cardiolipin is and why binding to it would do anything. Most of the people who write to us do not, and there is no shame in that. It is a corner of cell biology that barely gets a paragraph in most textbooks.

This article is our attempt to explain the mechanism the way we would to a new colleague over coffee. No equations. Six ideas, each building on the last. By the end you should be able to read a paper on MTP131 and follow the argument.

A note on the name: MTP131 is the same molecule as SS-31 and elamipretide. If the naming is new to you, our article on MTP-131 and its other names sorts it out.

Insight 1: Mitochondria make energy across a folded membrane

Start with the basics. A mitochondrion has two membranes. The outer one is a smooth bag. The inner one is heavily folded, and those folds are called cristae.

The inner membrane is where energy is made. Set into it are five large protein machines. Four of them, complexes I to IV, pass electrons down a chain and use the energy released to pump protons from the inside to the space between the membranes. That builds up a pressure of protons. The fifth machine, ATP synthase, lets the protons flow back and uses the flow to make ATP, the cell's energy currency.

Two things about this matter for our story.

The machines need to be close together and correctly lined up. Electrons have to hop from one to the next. If the complexes drift apart, electrons leak, and leaked electrons react with oxygen to form damaging reactive species.

The membrane has to be folded and sealed. The folds give more surface area and create small compartments where protons collect. If the folds flatten or the membrane gets leaky, the proton pressure falls and so does ATP output.

So the shape and organisation of the inner membrane are not decoration. They are part of how the thing works.

Insight 2: Cardiolipin is what holds that membrane together

Cardiolipin is a phospholipid, a fat molecule of the kind that makes up all cell membranes. It is an odd one. A normal phospholipid has one head and two fatty tails. Cardiolipin is essentially two of them joined at the head, so it has two phosphate groups and four tails.

That gives it three special properties.

It is cone-shaped, narrow at the head and wide at the tails. Cone-shaped lipids like to sit in curved membranes. Cardiolipin collects at the tight bends of the cristae and helps keep them bent.

It carries two negative charges. That lets it grip positively charged patches on proteins.

It is found almost nowhere except the inner mitochondrial membrane, where it makes up something like a fifth of the lipid.

Put these together and cardiolipin acts as a sort of glue and scaffold. It sits between the respiratory complexes and helps them assemble into larger units called supercomplexes. It binds to ATP synthase and helps it form the rows that shape the cristae tips. It anchors a small mobile protein called cytochrome c to the membrane surface so it can shuttle electrons between complex III and complex IV.

When cardiolipin is missing or abnormal, as in the genetic disease Barth syndrome, all of this falls apart to some degree. Cristae lose their shape. Supercomplexes come apart. Energy output drops.

Insight 3: Cardiolipin is easily damaged, and the damage feeds on itself

Here is the weak point. In heart and muscle, the four tails of cardiolipin are mostly linoleic acid, an unsaturated fat. Unsaturated fats are prone to oxidation. And cardiolipin sits right beside the electron transport chain, which is the main source of reactive oxygen species in the cell.

So the lipid that holds the energy machinery together is parked next to the thing most likely to damage it.

When cardiolipin is oxidised, it changes shape and no longer fits where it should. Complexes loosen. More electrons leak. More reactive species form. More cardiolipin is oxidised. It is a loop, and once it gets going it is hard to stop.

This loop is thought to turn in ageing, in tissue that has been starved of oxygen and then resupplied, in heart failure and in a range of other conditions. It is the reason cardiolipin became a target.

Insight 4: Cytochrome c has a dark side

This is the part of the story that surprised people. Cytochrome c is normally a well-behaved electron carrier. It sits loosely on the membrane surface, held by the charge on cardiolipin, and ferries electrons one at a time.

But cytochrome c can bind cardiolipin in a second, tighter way, in which one of the lipid's tails pushes into the protein. When that happens, the protein partly unfolds around its iron-containing core. In that state it stops being a carrier and becomes a peroxidase, an enzyme that uses hydrogen peroxide to oxidise things. And the thing nearest to hand is cardiolipin itself.

So under stress, cytochrome c turns on the very lipid that holds it in place. The oxidised cardiolipin lets go. Cytochrome c drifts off into the space between the membranes, and if the outer membrane becomes leaky, out into the cell, where it triggers programmed cell death.

That sequence, cardiolipin oxidation followed by cytochrome c release, is one of the early steps in apoptosis. It links a small change in a membrane lipid to the death of the whole cell.

Insight 5: What MTP131 does at the membrane

Now MTP131. MTP131 has four amino acids arranged as charged, aromatic, charged, aromatic, with three positive charges in total. We go through the structure in our article on elamipretide peptide chemistry.

Those positive charges are drawn to the negative charges on cardiolipin. The aromatic rings tuck into the oily part of the membrane just below the surface. The result is that MTP131 sits at the interface, lying along the membrane, in close contact with cardiolipin head groups.

A paper in 2013 showed this binding directly using fluorescent versions of MTP131 and went on to show what it does. Three effects are worth knowing.

It blocks the peroxidase switch

With MTP131 bound to cardiolipin, cytochrome c is less able to make the tight, tail-inserting contact that unfolds it. It stays in carrier mode. In the test tube, MTP131 strongly reduced the peroxidase activity of the cytochrome c and cardiolipin complex. That would break the loop described above at its key step.

It keeps electrons flowing

By holding cytochrome c in its normal state, and possibly by tidying the lipid environment around the complexes, MTP131 improved electron transfer and ATP production in mitochondria that had been stressed. In healthy mitochondria it did very little. That selectivity for stressed mitochondria comes up again and again in the literature.

It protects cristae structure

In animal models of kidney and heart injury, electron microscope images showed that mitochondria in treated tissue kept their folded inner membranes, while those in untreated tissue were swollen with broken cristae.

Insight 6: The picture has grown more detailed since

If the story stopped in 2013 it would be neat. It did not stop, and the newer work makes it richer and a bit less tidy.

One line of research looked at the electrical properties of the membrane surface. Cardiolipin makes the surface strongly negative, which attracts calcium and other positive ions. Too much calcium at the membrane is harmful. Studies published around 2020 showed that MTP131 tones down that surface charge and reduces the membrane's response to calcium, without disrupting the membrane itself. On this view MTP131 works partly as an electrostatic buffer.

Another study used chemical cross-linking in intact mitochondria to find out which proteins MTP131 sits next to. It found a dozen, falling into two groups: proteins involved directly in making ATP, and proteins involved in a branch of metabolism that feeds the electron transport chain. All of them are known to bind cardiolipin. That suggests MTP131 ends up at protein and cardiolipin contact points across the membrane.

Work in aged heart cells pointed to a specific protein, the adenine nucleotide translocator, which swaps ATP for ADP across the inner membrane. In old cells this protein leaks protons. MTP131 reduced that leak.

And the original antioxidant idea has not gone away. The dimethyltyrosine residue does scavenge reactive species directly. Most researchers now see that as a secondary contribution, but it is real.

So the honest summary is this. MTP131 binds cardiolipin. That much is well established. What follows from the binding is probably several things at once, and which matters most likely depends on the tissue and the kind of stress.

What this means if you are designing an experiment

Mechanism is only useful if it changes what you do at the bench. A few thoughts.

Stress your system

MTP131 does little in healthy mitochondria. If your cells are happy, well fed and unstressed, you may see nothing. Most positive studies used some kind of challenge: oxygen deprivation and return, oxidative stress, high glucose, ageing, a genetic defect.

Measure structure as well as function

Given that the proposed mechanism is about membrane organisation, readouts such as cristae shape on electron microscopy, supercomplex assembly on native gels or cardiolipin oxidation by mass spectrometry are directly relevant. Oxygen consumption alone may not tell the whole story.

Use the right control

SS-20 is a sister peptide without the dimethyltyrosine. It reaches mitochondria but lacks the radical-scavenging group, so it helps separate antioxidant effects from the rest. We describe it in our guide to the Szeto-Schiller peptide family.

Give it time

Binding is fast, minutes. Rebuilding membrane structure and letting cells recover is slower. Some of the most striking results in animals and in patients appeared only after weeks or months.

There is more on choosing models in our piece on Szeto Schiller 31 research models.

How MTP131 differs from other mitochondrial compounds

People often ask how this compares with MitoQ or SkQ1. Those are antioxidants attached to a positively charged carrier that is pulled into mitochondria by the membrane potential. They accumulate in the matrix, and they need a healthy membrane potential to get there.

MTP131 is different on both counts. Its uptake depends much less on membrane potential, so it still reaches depolarised, damaged mitochondria. And it stays at the inner membrane where cardiolipin is, not in the matrix.

Neither approach is better in the abstract. They do different things. But if your interest is the inner membrane and cardiolipin specifically, this is the more direct tool.

It also has nothing in common mechanistically with the other peptides we carry. BPC-157, TB-500, GHK-Cu and Retatrutide act through entirely separate pathways.

The link to Barth syndrome

It is worth closing the loop on the clinical side, because it is the best real-world test of the mechanism so far.

Barth syndrome is caused by loss of the enzyme that gives cardiolipin its mature set of tails. Patients have less normal cardiolipin and an abnormal intermediate form. Their mitochondria are structurally disorganised.

If MTP131 truly works by stabilising cardiolipin-dependent structure, this is where it should help most. After a long and difficult development, a pharmaceutical form was granted accelerated approval for Barth syndrome in the United States in 2025. We tell that story in our article on elamipretide.

That product is a prescription medicine. The material we sell is a research chemical for laboratory use only and is not for human or animal consumption.

Getting MTP131 for your lab

We list MTP131 as SS-31, in four purity grades.

• Standard Grade, 98 percent or better, for pilots and method work.
• High Purity Grade, for routine cell culture.
• Ultra-Pure Research Grade, 99.5 percent or better, with HPLC and mass spec.
• Bulk Research Grade, for labs running isolated mitochondria or tissue work at volume.

For mechanism studies where you may be making claims about a specific molecular interaction, we would lean toward the Ultra-Pure grade, since a reviewer may ask about impurities. For screening conditions, Standard is enough.

The minimum order is 50 units. Press Order beside any size on the SS-31 peptide page, add your quantity and delivery address, and we will reply by email with the total, usually the same day. Payment is by Apple Pay, Zelle, Chime, Cash App, USDT or Bitcoin. A Certificate of Analysis ships with every order, and you can ask to see it first through the contact page.

A way to picture it

If the detail above is hard to hold in your head, try this picture. It is not exact, but it is close enough to be useful.

Think of the inner membrane as a factory floor that has been folded up to fit more machines in. The machines are the respiratory complexes. They have to stand in a line, close together, so that parts can be passed from one to the next without being dropped.

Cardiolipin is the set of floor brackets that bolts each machine in place and keeps the floor folded. Take the brackets away, or let them rust, and the machines start to shift. Parts get dropped. Dropped parts are the leaked electrons, and they cause fires.

Cytochrome c is a worker who carries parts between two of the machines. Normally he holds on to a bracket lightly as he goes back and forth. Under bad conditions he grabs it too hard, changes his behaviour, and starts taking a hammer to the brackets instead.

MTP131 is a clip that fits over the bracket. With the clip on, the bracket is harder to damage, the worker cannot grab it the wrong way, and the machines stay where they should.

The picture breaks down if you push it. Lipids move, proteins breathe, and nothing in a membrane is bolted to anything. But as a first sketch of why a small peptide sitting on a lipid could affect energy output, it does the job.

Common misunderstandings about MTP131

We hear a handful of wrong ideas often enough to list them.

That it boosts healthy mitochondria. The evidence says otherwise. In study after study, MTP131 had little or no effect on mitochondria that were working normally. It appears to restore, not to enhance.

That it is just another antioxidant. If that were all, ordinary antioxidants would do the same job, and in most of the models tested they do not. The location and the lipid binding are what set it apart.

That it enters the mitochondrial matrix. It concentrates at the inner membrane. That is where cardiolipin is and where MTP131 stays.

That it replaces cardiolipin. It does not add lipid or repair the lipid chemically. It binds to what is there and changes how that lipid interacts with its neighbours.

That more is always better. Because binding is to a limited number of sites, there is no reason to expect ever-rising effects with ever-rising concentration. Several cell studies report a plateau, and a few report a bell shape. Run a range.

That it works instantly in every model. Uptake is fast. Functional recovery can take much longer, particularly where structure has to be rebuilt.

What is still not known

It would be wrong to give the impression that the mechanism is finished business. Some of the open questions:

How much of the effect comes from each of the proposed actions? Blocking cytochrome c peroxidase activity, tuning the surface charge, stabilising protein and lipid contacts and scavenging radicals have all been shown in one system or another. Nobody has cleanly separated them in a living tissue.

Does MTP131 bind other negatively charged lipids to a meaningful degree in cells? In model membranes it prefers cardiolipin, but real membranes are more complicated.

Why do some tissues respond more than others? Cardiolipin content and composition differ between heart, muscle, kidney and brain. That may be part of the answer.

What happens over months? Most mechanistic work looks at minutes to days. The clinical experience suggests the important changes may be slower.

These are good questions to be working on. The tools are available: cardiolipin lipidomics, native gels for supercomplexes, cryo-electron tomography for cristae, cross-linking mass spectrometry for neighbours. And MTP131 itself is simple to obtain and to handle, which is not true of many mechanistic probes.

Where to go from here

If this is your first reading on the subject, the next step is a primary paper. Pick the 2013 study that first showed MTP131 binding cardiolipin, read the figures before the text, and see whether the argument above matches what the data show. Then decide what you would measure in your own system.

Questions about MTP131 and cardiolipin

Does MTP131 bind anything other than cardiolipin?

It has the strongest affinity for cardiolipin among the membrane lipids tested, because of the double negative charge. Cross-linking studies show it close to several cardiolipin-binding proteins, which is likely a consequence of where it sits.

Is MTP131 an antioxidant?

Partly. It can scavenge reactive species through its dimethyltyrosine. Its main effect is now thought to be on membrane and protein organisation.

Why does it do so little in healthy cells?

Probably because in healthy mitochondria cardiolipin is intact and correctly placed, so there is little for MTP131 to rescue.

How quickly does MTP131 get into mitochondria?

Within minutes in cultured cells, according to the early uptake studies.

Where can I read the primary papers?

Search PubMed for SS-31 and cardiolipin. The 2013 and 2020 papers are the ones to start with.

In brief

The inner mitochondrial membrane has to be folded and organised to make energy. Cardiolipin keeps it that way and is easily damaged. Damaged cardiolipin turns cytochrome c into an enzyme that damages it further. MTP131 binds cardiolipin, interrupts that loop and helps the membrane hold its structure under stress.

That is the mechanism in six steps. For storage and handling once the vials arrive, see our SS-31 peptide storage guide.

MTP-131 is a name that sends people in circles. A researcher finds a paper about a compound called MTP-131, goes looking for somewhere to buy it, and finds almost nothing. Or they find it listed next to SS-31 and elamipretide at three different prices and assume they are three different things. They are not. It is one molecule that has been renamed more often than most people change jobs.

We field this question so regularly that it seemed worth writing the whole thing down once. Here is where each name came from, when it was used, and how to make sure a literature search or a purchase order is pointing at the right compound.

The short answer on MTP-131

MTP-131 is the development code that Stealth Peptides, later Stealth BioTherapeutics, gave to the tetrapeptide D-Arg-Dmt-Lys-Phe-NH2. The same molecule is also called:

• SS-31, its original laboratory name.
• Bendavia, an early brand name used in clinical trials.
• Elamipretide, the official international non-proprietary name.
• Ocuvia, used for an eye-drop formulation.
• Forzinity, the brand name of the pharmaceutical product approved in 2025.

Six labels if you count the last. One structure. One CAS number, 736992-21-5. One molecular weight, 639.8 g/mol.

If you remember nothing else from this page, remember the CAS number. Names drift. The registry number does not.

Name 1: SS-31, where it started

The compound was first described in the early 2000s by Hazel Szeto in New York and Peter Schiller in Montreal. They had made a series of small peptides and numbered them. SS for Szeto and Schiller, 31 for its position in the list.

Papers from the academic labs, especially from Szeto's own group and her collaborators, have used SS-31 throughout, right up to the present. If you are reading basic science on mechanism, on cardiolipin binding or on ageing in mice, this is the name you will mostly see.

It is also the name the research supply trade uses. That is why our own product page is headed SS-31 peptide and not MTP-131. More on the origins is in our essential facts about SS-31.

Name 2: MTP-131, the company code

When a company licenses a compound, it gives it an internal code. Codes are neutral, they do not presume a brand, and they let the company talk about a programme before any official name exists.

Stealth Peptides was founded in 2006 to develop the Szeto-Schiller compounds. MTP is generally read as mitochondria-targeted peptide. The number has no special meaning that we know of.

MTP-131 shows up in the literature from roughly 2010 onward, mainly in three kinds of document. Company-sponsored preclinical studies. Conference abstracts. And clinical trial registrations, where a code is often used because the generic name has not yet been assigned.

A few examples of work published under or alongside this code:

• Studies in rats showing protection of the kidney after blood flow was cut off and restored.
• Studies in mice with heart muscle disease driven by high blood pressure hormones.
• A study in dogs with advanced heart failure, where three months of treatment improved heart function and mitochondrial measures.
• Early human pharmacology studies in healthy volunteers.

You will sometimes see it written MTP131 with no hyphen. Same thing. We look at the mechanism work under that spelling in our article on MTP131 and cardiolipin.

Name 3: Bendavia, the brand that did not last

For its first clinical programme, in heart attack patients, the company used the brand name Bendavia. The trial was EMBRACE STEMI, and the published report refers to the drug as Bendavia and as MTP-131 in the same breath.

The name was used for a few years across cardiac and kidney trials and then quietly retired. Brand names chosen early in development often are. If you come across Bendavia in a paper from around 2012 to 2016, you are reading about the same compound.

Name 4: Elamipretide, the official one

Every drug that reaches a certain stage is given an international non-proprietary name by the World Health Organization, with a matching United States Adopted Name. These are the generic names, the ones that do not belong to any company.

The name assigned was elamipretide. The ending, -tide, marks it as a peptide. From about 2016, trial reports and reviews switched to it, and it is now the standard term in clinical writing. Our article on elamipretide tells the clinical story under that name, including the trials that did not work.

A search for the generic name alone will miss most of the earlier work. That is the trap.

Name 5: Ocuvia and Forzinity

Ocuvia was a topical eye formulation tested in early trials for eye diseases. Later eye studies used injections under the skin and dropped the separate name.

Forzinity is the brand name under which a pharmaceutical form received accelerated approval from the US Food and Drug Administration in September 2025 for Barth syndrome. Details are in the FDA trial snapshot. That is a prescription medicine. It has nothing to do with research-grade material other than sharing the same active molecule.

Why the names matter when you search

Here is a test you can try. Go to PubMed and search for elamipretide. Note the number of results. Then search for SS-31. Then MTP-131. Then Bendavia. The four lists overlap but none contains all of the others.

Databases have got better at linking synonyms, but they are not perfect, and older records were indexed under whatever term the authors used. If you search one name, you will miss papers.

The fix is to search them all at once. In PubMed:

• elamipretide OR SS-31 OR MTP-131 OR Bendavia

You can run that combined search here. For trial records, the same approach works on ClinicalTrials.gov, which lists registered studies under several of the names.

Two more tips. Put SS-31 in quotation marks, or the search engine may split it at the hyphen and return every paper that mentions SS and 31. And watch out for SS-20 and SS-02, which are sister compounds, not synonyms. We explain those in our guide to the Szeto-Schiller peptide family.

Why the names matter when you buy

This is where confusion costs money.

A supplier that lists MTP-131, SS-31 and elamipretide as three separate catalogue items, with three prices, is either padding the catalogue or does not understand the product. Neither is reassuring. One compound should have one listing, with the other names given as synonyms.

When you place an order, name the compound and give the CAS number. If the supplier's paperwork shows a different CAS number, stop. If the Certificate of Analysis gives a molecular weight other than 639.8 for the free base, stop. Those two checks catch almost every mix-up.

Also check the sequence on the COA. It should read D-Arg-Dmt-Lys-Phe-NH2. There is a sister compound, SS-20, with the sequence Phe-D-Arg-Phe-Lys-NH2 and a different mass. It is a legitimate research compound in its own right, often used as a control, but it is not what you want if you ordered MTP-131.

What the MTP-131 literature actually showed

Since you may have arrived here from a paper, a quick map of the preclinical work published under this name is useful. We are summarising, not endorsing. Read the originals.

Kidney

In rat models, giving the compound before or shortly after a period of interrupted blood flow preserved the structure of mitochondria in kidney tubule cells and sped up recovery of ATP. Later studies looked at longer-term scarring. This body of work is where the cardiolipin mechanism was first laid out clearly, in 2013.

Heart

Mouse studies looked at heart enlargement and failure caused by angiotensin and by pressure overload. The dog study is the one most often cited: animals with heart failure induced by repeated tiny blockages of the coronary vessels were treated for three months and showed better pumping function, along with improved mitochondrial respiration in heart tissue.

Skeletal muscle

In aged mice, a single treatment was reported to restore mitochondrial energy output in leg muscle toward that of young animals within an hour, with improved fatigue resistance after a week. This 2013 paper is probably the most quoted one in the ageing field.

Eye and brain

Smaller numbers of studies looked at retinal cells under oxidative stress and at models of neurodegeneration.

What ties these together is that the compound seems to do most in mitochondria that are already under stress and least in healthy ones. That is a useful thing to know when choosing controls. There is more on study design in our piece on Szeto Schiller 31 research models.

From animals to people: where MTP-131 fell short

It would be misleading to stop at the animal data. The first large human trial, in heart attack patients, did not reduce the size of the damaged area. A four-week trial in heart failure did not improve heart dimensions. A Phase 3 trial in mitochondrial muscle disease missed both main endpoints.

The one clear clinical success came in Barth syndrome, a rare genetic disease of cardiolipin remodelling, and only after long-term follow-up.

For laboratory researchers, the gap between animal and human results is not a reason to dismiss the compound. It is a reason to design carefully, treat for long enough, and measure more than one thing.

How we label it

On our site and on our vials, the compound is called SS-31, with elamipretide given as the synonym. The Certificate of Analysis states the sequence, the molecular weight and the lot number. If your purchasing system or your paperwork needs it described as MTP-131, tell us and we will add that to the documents. It is a common request from institutions whose protocols were written around a particular paper.

We stock it in four grades.

• Standard Grade, from 5 mg, 98 percent or better.
• High Purity Grade, for routine cell work.
• Ultra-Pure Research Grade, 99.5 percent or better, verified by HPLC and mass spectrometry.
• Bulk Research Grade, in 100 mg, 250 mg and 500 mg vials.

If you are not sure which fits, our SS31 buying guide walks through the choice.

Ordering MTP-131 for research

We are a wholesale supplier. The minimum order is 50 units, mixed grades and sizes allowed, and other compounds in our catalogue count toward it. Those are BPC-157, GHK-Cu, Retatrutide and TB-500.

The process:

• Open the SS-31 peptide page and press Order beside the size you want.
• Enter the number of units and your delivery address.
• Choose a payment method: Apple Pay, Zelle, Chime, Cash App, USDT or Bitcoin.
• We reply by email, usually within the day, with the total and payment details.

Every order ships with the COA for its lot. If you want to see it first, ask in the message box or through the contact page.

All material is sold for laboratory and in-vitro research only. It is not for human or animal use, and we do not give advice on dosing.

Reading an older paper: a translation guide

If you have a paper open that uses MTP-131 and you want to connect it to something more recent, these pointers help.

Check the sequence. Somewhere in the methods, usually the first paragraph, the authors will give it. If it says D-Arg-Dmt-Lys-Phe-NH2, or D-Arg-2,6-dimethyltyrosine-Lys-Phe-NH2, you are reading about the same compound sold today as SS-31.

Check the supplier line. Papers from this period often say the material was provided by Stealth Peptides or Stealth BioTherapeutics. That confirms it is the company's own MTP-131 and not a look-alike.

Check how it was given. Company-sponsored animal studies generally used injection under the skin or infusion into a vein. Academic studies more often used injection into the abdomen or delivery by a small implanted pump. The route affects how results compare.

Check the units. Some papers give doses by weight of the salt, some by weight of the free peptide, and many do not say which. When two studies of MTP-131 seem to disagree on dose, this is often the reason.

Check the date against the trial history. A preclinical paper from 2012 was written when hopes were high and no large trial had reported. A paper from 2020 was written with the knowledge that several had missed. The tone of the discussion sections changes accordingly, and it is worth reading both with that in mind.

How to refer to the compound in your own work

If you are writing up research, you have to choose a name. Our suggestion, for what it is worth:

In a basic science paper, use SS-31 at first mention and give the alternatives in brackets: SS-31, also known as elamipretide and MTP-131. Then use SS-31 throughout. That matches the mechanistic literature your readers will know.

In a clinical or translational paper, lead with elamipretide and give SS-31 and MTP-131 as synonyms.

In either case, state the sequence, the CAS number and the supplier, grade and lot in the methods. It takes two lines and removes all doubt. Reviewers increasingly ask for it, and readers trying to repeat your work will thank you.

Put all the names in your keywords. Someone searching in five years may use any of them, and you want to be found.

Other codes you might run into

A few more labels turn up around MTP-131 and cause confusion.

SBT numbers. The same company later used an SBT prefix for other compounds in its pipeline. Those are different molecules, some of them newer relatives designed to improve on the original. A paper about an SBT compound is not about this one unless it says so.

SS-20. A sister peptide, not a synonym. It lacks the dimethyltyrosine and is mainly used as a control.

SS-02. Another relative, with strong opioid activity. Definitely not interchangeable.

MTP-101, MTP-151 and similar. You may occasionally see other MTP numbers in old abstracts or patents. They refer to other candidates from the same programme.

Brand names on supplement sites. Now and then a product appears with a name that sounds related and a label hinting at mitochondria. Unless the sequence and CAS number are stated and match, treat it as unrelated.

The rule is the same every time. Names are marketing, history or habit. The sequence and the registry number are chemistry. When in doubt, go back to those.

Why we care about getting this right

It might seem like a lot of words about labels. Here is why it matters to us. Every month we hear from someone who bought what they thought was MTP-131 elsewhere, could not match it to the paper they were following, and lost weeks working out whether the fault was in the compound or the experiment. Almost always the compound was fine and the confusion was in the naming. Ten minutes with the CAS number would have saved them.

A short history of how drug codes work

It may help to know that MTP-131 is a typical example of a wider habit, not an oddity. Almost every drug candidate goes through the same sequence of labels.

First comes a laboratory name, chosen by the scientists. It might be initials and a number, as here, or a compound number from a screening library. It appears in the early academic papers and tends to stick among researchers.

Next comes a company code, once someone licenses the molecule. Two to four letters for the company or programme and a number. Codes are deliberately bland. They do not promise anything, they are easy to trademark around, and they let a company discuss a programme before any generic name exists. MTP-131 belongs to this stage.

Then a brand name may be tried out for trials, and may or may not survive to market.

Then an official generic name is assigned, built from standard stems that tell pharmacists what class the drug belongs to.

Finally, if the drug is approved, a marketed brand name goes on the box.

So a molecule that reaches the pharmacy commonly has four or five names by the time it gets there. The research supply trade usually settles on the first, the laboratory name, because that is what the people ordering it read in the papers. This is why you will find SS-31 on a supplier's price list and MTP-131 in a trial registry, and why knowing the full set of names is part of knowing the compound.

What we check when a customer asks for MTP-131 by name

When an enquiry comes in asking for MTP-131, we do three things before quoting. We confirm with the customer that they mean the tetrapeptide with CAS number 736992-21-5. We ask which paper or protocol they are following, because that often tells us which grade suits them. And we note on the order that the documents should carry MTP-131 as a synonym, so that the paperwork matches what their records expect. It adds a few minutes and avoids confusion later.

Questions we hear about MTP-131

Is MTP-131 the same as SS-31?

Yes. MTP-131 is the company development code for the compound first published as SS-31.

Is MTP-131 the same as elamipretide?

Yes. Elamipretide is the generic name assigned later to the same molecule.

Why can I not find MTP-131 for sale under that name?

Because research suppliers almost all list it as SS-31. Search for that, and confirm with the CAS number 736992-21-5.

What does MTP stand for?

It is generally taken to mean mitochondria-targeted peptide. It was a company code, not a scientific term.

Is MTP-131 different from MTP131?

No. The hyphen is a matter of style. Some papers and databases drop it.

How should I store it?

Dry, at minus 20, in the dark. Our SS-31 peptide storage guide has the full routine.

Summing up

One molecule, several names, picked up at different stages of a long development. SS-31 in the academic lab. MTP-131 inside the company. Bendavia in the first trials. Elamipretide as the official generic. Forzinity on the pharmacy label.

Search with all of them. Buy by CAS number. Check the sequence and the mass on the certificate. And if a seller tries to charge you three prices for three names, you know what to do.

For a neutral overview of the compound, the Wikipedia article on elamipretide is a reasonable starting point. For current sizes and prices, see our SS-31 peptide page.

The elamipretide peptide is four amino acids long. You would think there was not much to say about the chemistry of something that small. There is, and most of it has direct consequences for anyone who weighs it out, dissolves it or tries to work out what concentration they actually have in the tube.

We get chemistry questions from customers every week. Some come from peptide chemists who know more than we do. Most come from biologists who are perfectly good at their own work and were never taught why a 10 mg vial might hold 7.8 mg of peptide. This article is for them. Seven facts, each tied to something practical.

Fact 1: The sequence is short, and every position is doing a job

The elamipretide peptide has the sequence D-Arg-Dmt-Lys-Phe-NH2. Reading from the start:

• D-arginine. Positively charged, and in the mirror-image form.
• Dmt, or 2,6-dimethyl-L-tyrosine. Aromatic, with a phenol group.
• Lysine. Positively charged.
• Phenylalanine. Aromatic.
• An amide cap on the end, where a free acid would normally be.

So the pattern is charged, aromatic, charged, aromatic. That alternation is the defining feature of the whole Szeto-Schiller series, and it is what lets these peptides cross membranes and settle on the inner mitochondrial membrane. Change the order and the behaviour changes. We describe the sister compounds in our guide to the Szeto-Schiller peptide family.

The molecular formula is C32H49N9O5. The average molecular weight is 639.8 g/mol. Those two numbers are worth writing on the inside cover of your lab book, because you will need them.

Fact 2: Two of the four residues are not natural, on purpose

Ordinary peptides do not last long in biological systems. Enzymes called peptidases cut them up within minutes. The designers of the elamipretide peptide dealt with that in three ways.

First, the D-arginine at position one. Peptidases evolved to recognise L-amino acids. Put a D-residue at the front and the enzymes that chew peptides from the N-terminus cannot get a grip.

Second, the amide at the C-terminus. Enzymes that attack from the other end look for a free carboxylic acid. There is none.

Third, the dimethyltyrosine. The two methyl groups sit either side of the ring and crowd the neighbouring peptide bonds, which makes them harder to reach. They also change the electronic character of the phenol, making it better at donating a hydrogen atom to a free radical. That is the basis of the molecule's direct antioxidant activity.

The practical result is a peptide that is far more stable than its size suggests. In your tube of culture medium, it will still be there tomorrow. For most short peptides you could not assume that.

Dmt is also the expensive part. It is not a commodity amino acid. A good share of the cost of making this compound is the cost of that one building block.

Fact 3: It carries three positive charges, and that shapes everything

At neutral pH, the elamipretide peptide has a net charge of plus three. One comes from the guanidinium group on arginine, one from the side-chain amine on lysine, and one from the free amine at the N-terminus. There is nothing negative to balance them, because the C-terminus is capped.

Three charges on a molecule of 640 daltons is a high charge density. Several things follow.

It is extremely soluble in water. You do not need organic solvent, acid or heat. If someone tells you to dissolve it in DMSO first, they are following a habit from other compounds.

It is attracted to negatively charged surfaces. That is how it finds cardiolipin, which carries two negative charges. It is also why very dilute solutions lose peptide to glass and to some plastics. Use polypropylene, preferably low-binding, and keep stocks reasonably concentrated.

It always comes with counter-ions. Three positive charges need three negative partners. This is the part that causes the most confusion, so it gets its own section.

Fact 4: What you weigh is a salt, not the bare peptide

You cannot bottle a positively charged molecule on its own. Every vial of elamipretide peptide contains the elamipretide peptide plus whatever negative ions came along with it through purification.

There are three common salt forms.

Trifluoroacetate

TFA is used in the standard purification method, so the elamipretide peptide comes off the column as a TFA salt by default. Three TFA ions weigh 342 between them. Added to 639.8, that gives a salt weighing about 982. The elamipretide peptide itself is only about 65 percent of that.

Acetate

Many suppliers swap TFA for acetate, which is gentler on cells. Three acetates weigh 180, for a salt of about 820. The elamipretide peptide is roughly 78 percent.

Hydrochloride

Chloride is small. Three of them, with their protons, add about 109, for a salt of roughly 749. The elamipretide peptide is about 85 percent. The approved pharmaceutical form is a hydrochloride salt.

On top of the counter-ion there is always a little residual water, typically a few percent, because freeze-dried peptides hold on to it.

Put it together and the same 10 mg of powder might contain 6.2 mg of peptide as a TFA salt, 7.5 mg as an acetate or 8.2 mg as a hydrochloride. That is a spread of 30 percent in your final concentration, from something that never appears in the HPLC purity figure.

Fact 5: Net peptide content is the number you actually need

HPLC purity tells you what fraction of the elamipretide peptide-like material is the right peptide. Net peptide content tells you what fraction of the powder is peptide at all. They are different questions.

Net content is measured by amino acid analysis or by elemental nitrogen analysis. Not every supplier does it on every lot, because it costs more than HPLC. But a supplier should at least be able to tell you the salt form, and from that you can estimate.

Here is how to use it. Say you want a 1 millimolar stock and your vial holds 10 mg of acetate salt at 78 percent net content.

• Peptide present: 10 mg times 0.78, which is 7.8 mg.
• Moles: 7.8 mg divided by 639.8 mg per millimole, which is 0.0122 millimoles.
• Volume for 1 millimolar: 12.2 millilitres.

If you had ignored the salt and used 10 mg, you would have added 15.6 millilitres and ended up 22 percent weaker than you thought. In a dose-response experiment that shifts the whole curve.

The other approach is to ask whether the vial is filled by net peptide weight. Some are. Then 10 mg means 10 mg of peptide and the sum is simpler. Either convention is fine. What is not fine is not knowing which one applies. We answer this for any lot on request through the contact page, and there is more on reading the paperwork in our piece on SS31 peptide purity testing.

Fact 6: How the elamipretide peptide is made

At research scale the usual route is solid-phase peptide synthesis. The process runs backwards, from the C-terminus to the N-terminus.

You start with resin beads carrying a linker that will leave an amide when cut. Phenylalanine goes on first. Its protecting group is removed, lysine is coupled, then Dmt, then D-arginine. Each amino acid carries temporary protection on its reactive groups so that it joins only where intended. At the end, a strong acid cocktail cuts the elamipretide peptide off the resin and strips the side-chain protection in one step.

What comes off is crude. Typically 70 to 90 percent of it is the right product. The rest is deletion sequences, fragments, and peptide with protecting groups still attached. Arginine's protecting group is the slowest to leave and the most common source of a late-running impurity.

Purification is by preparative reverse-phase HPLC. The crude mixture goes onto a large column, the components separate, and the fractions containing the target are collected, pooled and checked. Then salt exchange if required, then freeze-drying.

Because there are only three coupling steps, the crude material is cleaner than for longer peptides, and purification to 99 percent or above is routine in competent hands. For larger scale manufacture, a short peptide like this can also be made in solution without a resin, which is cheaper per kilo.

Fact 7: Stability is good, with two things to watch

The elamipretide peptide has no methionine, no cysteine, no tryptophan, no asparagine and no glutamine. Those are the residues that cause most peptide stability problems, through oxidation, disulfide scrambling or deamidation. Their absence is a large part of why this compound is easy to live with.

The two things to keep in mind:

The Dmt phenol can oxidise. It is designed to react with radicals, after all. Under normal storage, dry and cold and dark, this is very slow. In solution, in the light, with dissolved oxygen and trace metals around, it is faster. Keep stocks cold and covered.

The dry powder takes up water. All freeze-dried peptide salts do, and a highly charged one does it readily. An opened vial left on the bench in a humid room will gain weight within minutes. That does not destroy the elamipretide peptide, but it throws off your weighing and brings in the water that every other degradation pathway needs.

The handling routine that deals with both is in our SS-31 peptide storage guide. In short: dry at minus 20, warm the vial before opening, dissolve only what you need, and aliquot.

Analysing the elamipretide peptide

If you want to check a lot yourself, the compound is straightforward to analyse.

By reverse-phase HPLC on a C18 column, with water and acetonitrile containing 0.1 percent TFA, it elutes early because it is so polar. Start the gradient at five percent organic or lower. Detect at 214 or 220 nanometres. The Dmt ring also absorbs around 275 to 280, which is useful as a second wavelength.

By electrospray mass spectrometry you will see the singly charged ion at about 640.4 and the doubly charged ion at about 320.7. The doubly charged one is often the stronger signal, which catches people out when they go looking only for 640. A triply charged ion near 214 may also show.

If you see a peak 16 mass units heavier than expected, that is oxidation. A peak lighter by the mass of one residue is a deletion sequence. A peak about 252 heavier points to an arginine protecting group that never came off. Knowing these three covers most of what turns up.

How this compares with the other peptides we stock

The same principles apply across our catalogue, with different numbers.

BPC-157 is 15 residues with several acidic groups, so its net charge is close to neutral or negative, and its salt behaviour is quite different. GHK-Cu is a tripeptide bound to copper, so the metal is part of what you weigh. TB-500 is 43 residues, and its net peptide content tends to be higher simply because counter-ions are a smaller share of a larger molecule. Retatrutide carries a fatty acid side chain that makes it behave almost like a detergent.

If you move between these in the lab, do not carry assumptions from one to the next. Check the salt form and net content each time.

Which grade of elamipretide peptide to order

Chemistry informs this choice as well. The grades differ in HPLC purity, which is to say in how much related peptide impurity is present.

• Standard Grade, 98 percent or better. Up to two percent of deletion sequences and similar.
• High Purity Grade. A tighter cut for routine work.
• Ultra-Pure Research Grade, 99.5 percent or better, with mass confirmation. For quantitative or analytical work.
• Bulk Research Grade, 99 percent or better, in vials up to 500 mg.

For most cell experiments, the uncertainty from salt form and pipetting is larger than the difference between 99.0 and 99.5 percent purity. Spend your attention on getting the concentration right first. Our SS31 buying guide goes through the decision in more detail.

Ordering

We sell wholesale from a minimum of 50 units. Open the SS-31 peptide page, press Order next to the grade and size you want, and add your quantity and delivery address. If you need the salt form, net content or COA for the current lot, ask in the message and we will send it with the quote, normally the same day. Payment is by Apple Pay, Zelle, Chime, Cash App, USDT or Bitcoin.

All material is for laboratory research only. It is not for human or animal use.

Worked sums for common vial sizes

Most questions we get about the elamipretide peptide come down to arithmetic. Here are the figures for the sizes we sell, assuming an acetate salt with 78 percent net content. If your lot is different, swap in your own number.

A 5 mg vial holds about 3.9 mg of peptide, which is 6.1 micromoles. Add 6.1 ml of water for a 1 millimolar stock, or 0.61 ml for 10 millimolar.

A 10 mg vial holds about 7.8 mg, or 12.2 micromoles. That needs 12.2 ml for 1 millimolar, 1.22 ml for 10 millimolar.

A 25 mg vial holds about 19.5 mg, or 30.5 micromoles. 3.05 ml gives 10 millimolar.

A 50 mg vial holds about 39 mg, or 61 micromoles. 6.1 ml gives 10 millimolar.

If you prefer to work in mass per volume, it is simpler still. Add 1 ml to a 10 mg vial and you have 10 mg per ml of salt, or 7.8 mg per ml of elamipretide peptide. Decide which of those two you mean, write it on the tube, and stick with it. Half the confusion between labs comes from one group quoting salt weight and the other quoting peptide weight for what they both call the same concentration.

To go from a 10 millimolar stock to a working concentration, the dilutions are large. One microlitre of stock in 10 ml of medium gives 1 micromolar. For anything lower, make an intermediate dilution first. Pipetting a tenth of a microlitre is not a real measurement.

pH, buffers and what the elamipretide peptide does in them

Dissolved in plain water, the elamipretide peptide gives a mildly acidic solution, because the counter-ions bring a little acid with them. An acetate salt will sit around pH 5 to 6. A TFA salt can be lower. That is fine for a stock. It may not be fine if you add a large volume of it to a weakly buffered assay.

In practice the stock is diluted so far that the medium or buffer sets the pH, and there is nothing to adjust. If you are working at high concentration, in isolated mitochondria for example, check the pH after adding the elamipretide peptide and correct it if needed.

Phosphate buffered saline, HEPES and Tris are all compatible. The elamipretide peptide has no free carboxyl group and no histidine, so it does not chelate metals to any great extent and does not interfere with common buffers.

One thing to watch for is binding to negatively charged material. Heparin, nucleic acids and some serum proteins carry negative charge and will hold on to a share of any strongly positive peptide. In serum-containing medium, the free concentration of elamipretide peptide will be somewhat lower than the nominal one. For most experiments that does not matter. For quantitative binding work it might, and serum-free conditions are cleaner.

Why the Dmt residue is hard to make

A question that comes up from chemists: why is dimethyltyrosine so expensive?

Tyrosine is cheap because organisms make it by the tonne. Dimethyltyrosine has to be built by synthesis. Two methyl groups must be placed on the aromatic ring at exactly the positions next to the side chain, and the amino acid must come out as a single mirror-image form. Both requirements add steps and cut yield.

It then has to be protected for peptide synthesis, which is another couple of steps. And it couples more slowly than an ordinary amino acid because those two methyl groups get in the way, so the synthesis needs longer reaction times or stronger coupling reagents at that position.

None of this is beyond a competent peptide lab. It does mean that a supplier cutting corners has an obvious place to cut them. A batch of elamipretide peptide made with poor quality Dmt, or with the Dmt coupling rushed, will carry a recognisable deletion impurity that is missing that residue. It shows up in the mass spectrum at 191 mass units below the main signal. If you ever see that peak at more than trace level, you know what happened.

One habit worth forming

Every time you open a new lot of the elamipretide peptide, write three things on the first page of your notes: the salt form, the net content and whether the vial is filled by gross or net weight. It takes a minute. It removes the most common source of error in work with this compound, and it means anyone reading your notes later can reproduce your concentrations exactly.

Questions about elamipretide peptide chemistry

What is the molecular weight of the elamipretide peptide?

639.8 g/mol for the free base. The salt you weigh will be heavier, depending on the counter-ion.

Is the elamipretide peptide soluble in water?

Very. It is one of the most water-soluble peptides you will handle.

Does the counter-ion affect my experiment?

It can. TFA at high concentration can affect some cell assays. Acetate and chloride are generally considered benign. At the dilutions used in most experiments, the amounts are tiny.

Why does my mass spectrum show 320 and not 640?

That is the doubly charged ion. With three basic sites, the molecule picks up two protons easily. It is the same compound.

Is SS-31 chemically identical to the elamipretide peptide?

Yes. Same sequence, same structure. Only the name differs. See our essential facts about SS-31 or the Wikipedia article.

Summary

Four residues, two of them unusual, three positive charges, one amide cap. Very soluble, very stable, always sold as a salt. The salt and the water mean that powder weight is not peptide weight, and correcting for that is the single most useful bit of chemistry a biologist can take from this page.

If anything here raises a question about a specific lot, write to us. We would much rather answer it before the experiment than after.

Elamipretide took about twenty years to get from a university lab to a pharmacy shelf, and for most of that time it looked like it would not make it. Trials missed their targets. A regulator refused to even review the application. The company behind it nearly ran out of road more than once. Then, in September 2025, it was approved.

We sell the research-grade form of this molecule, so we have followed the story closely, partly out of professional interest and partly because customers ask us about it all the time. What follows is the history as we understand it, failures included. If you are planning research with elamipretide, knowing where it stumbled is at least as useful as knowing where it worked.

One thing up front. What we sell is a laboratory chemical for in-vitro research. It is not the approved medicine, and nothing here is advice about treatment.

Where elamipretide came from

The molecule was first made in the early 2000s by Hazel Szeto at Weill Cornell Medical College and Peter Schiller at the Clinical Research Institute of Montreal. They called it SS-31, after their initials and its place in a numbered series. We wrote about the rest of that series in our guide to the Szeto-Schiller peptide family.

The two were not looking for a mitochondrial drug. They were making analogues of opioid peptides. Along the way they found that certain small peptides with alternating aromatic and positively charged amino acids could cross cell membranes and collect in mitochondria. A 2004 paper in the Journal of Biological Chemistry described the effect and showed that these peptides protected cells and tissue from oxidative damage.

That paper is where the story really starts. It reported a compound that got into mitochondria without depending on the membrane's electrical charge, which meant it could reach sick mitochondria as well as healthy ones. Nobody had a good tool for that at the time.

From SS-31 to MTP-131 to Bendavia to elamipretide

In 2006 a company called Stealth Peptides was set up to develop elamipretide. It licensed the rights from Cornell and from the Montreal institute. The company later renamed itself Stealth BioTherapeutics.

The molecule picked up names as it went. Inside the company it was MTP-131. For early clinical work it carried the brand name Bendavia. When it was assigned an international non-proprietary name, that name was elamipretide. Ocular formulations were sometimes called Ocuvia.

If you search the literature you need all of these. A 2010 paper will say SS-31. A 2014 trial registration will say Bendavia or MTP-131. Anything after about 2016 will say elamipretide. They are one compound. We untangle the naming in more detail in our article on MTP-131.

The first big test: heart attacks

The early animal data were strongest in ischaemia-reperfusion injury. That is the damage done when blood supply to a tissue is cut off and then restored, as happens when a blocked coronary artery is reopened after a heart attack. Much of that damage comes from mitochondria, so it was a logical place to start.

The trial was called EMBRACE STEMI. Patients having a first heart attack were given elamipretide or placebo by infusion around the time their artery was reopened. The main measure was the size of the damaged area of heart muscle.

Results were published in 2016. Elamipretide was safe and well tolerated. It did not reduce infarct size. The primary endpoint was missed.

This was a blow, but not an unusual one. Cardioprotection is a graveyard for promising compounds. Dozens of things that shrink infarcts in animals have failed in people. Timing is brutally hard, patients differ, and a single short infusion may simply be too little. The trial did not show the mechanism was wrong. It showed that this way of testing it did not work.

Heart failure: a hint, then nothing

The company moved on to chronic heart failure, where failing mitochondria are part of the picture and treatment can be given over weeks, not minutes.

A small early study gave a single infusion to patients with heart failure and reduced ejection fraction. At the highest dose, heart volumes improved over a few hours. That was encouraging enough to run a longer study.

The follow-up gave elamipretide by daily injection under the skin for four weeks. It did not improve the primary measure of heart size compared with placebo.

Two cardiac programmes, two misses. By this point a less stubborn company might have stopped.

Primary mitochondrial myopathy and the MMPOWER trials

The next target made more obvious sense. Primary mitochondrial myopathies are genetic diseases in which the mitochondria themselves are faulty. Patients have muscle weakness, fatigue and poor exercise tolerance. There were no approved treatments.

Early studies, known as MMPOWER and MMPOWER-2, were small and short. They suggested patients could walk further in six minutes after a few days of treatment. On the strength of that, a Phase 3 trial called MMPOWER-3 enrolled more than two hundred patients for 24 weeks of daily injections.

The results came at the end of 2019. The trial missed both of its primary endpoints. Walking distance and fatigue scores were no better on drug than on placebo.

This was the lowest point. A Phase 3 failure in the disease that seemed the best fit. But there was a wrinkle. When the data were broken down by the genetic cause of each patient's disease, those with defects in nuclear genes, particularly genes involved in copying mitochondrial DNA, appeared to respond, while those with defects in mitochondrial DNA itself did not. Subgroup findings like this are notoriously unreliable. The company chose to test it properly in a new trial restricted to that group. That work was still going on at the time of writing.

Barth syndrome: the indication that fit

Barth syndrome is very rare. It affects boys and men almost exclusively, and only a few hundred are known worldwide. It is caused by mutations in a gene called TAZ, which codes for an enzyme that remodels cardiolipin. Without it, cardiolipin is abnormal, mitochondria work poorly, and patients develop heart muscle disease, skeletal muscle weakness and severe fatigue. Many die young.

By the mid 2010s, research had shown that the molecule binds to cardiolipin. A disease defined by broken cardiolipin was about as direct a match as could be imagined.

The trial, TAZPOWER, was tiny because the disease is tiny. Twelve patients. Each received elamipretide and placebo in turn for twelve weeks, in random order. At the end of that blinded phase there was no significant difference.

Then the patients carried on taking elamipretide in an open-label extension. Over the following months, and then years, their walking distance and muscle strength improved steadily, and measures of heart function improved too. The company also compared these patients with historical records of untreated patients, who do not get better on their own.

The long fight with the regulator

This is where it got difficult. The US Food and Drug Administration generally wants to see a benefit in the blinded, placebo-controlled part of a trial. TAZPOWER had not shown one. The improvement came later, in the unblinded part, where patients and doctors knew what was being given.

The company argued that twelve weeks had simply been too short for muscle to rebuild, and that a larger or longer placebo-controlled trial was not feasible in a disease with so few patients. The agency was not persuaded at first. In 2021 it declined to accept the application for review.

Patients and families pushed hard. The company went back with more follow-up data. An application was eventually accepted, and in late 2024 an advisory committee of outside experts voted narrowly that elamipretide was effective. Even then the agency did not approve it straight away. In 2025 it issued a letter declining approval in the form requested but pointing toward the accelerated approval route, which allows a drug to be approved on an intermediate measure likely to predict benefit, with confirmation required afterwards.

In September 2025, elamipretide received accelerated approval for Barth syndrome under the brand name Forzinity. It was the first treatment ever approved for the disease and the first approved drug designed to act on mitochondria. The FDA trial snapshot sets out the basis for the decision.

The eye programme

Running alongside all of this was work on dry age-related macular degeneration. The cells of the retina are among the most energy-hungry in the body, and mitochondrial decline is thought to contribute to their loss.

A Phase 2 trial called ReCLAIM-2 gave daily injections under the skin for 48 weeks to patients with an advanced form of the disease. It missed its two primary endpoints. However, a structural measure of photoreceptor health did favour elamipretide, and more treated patients gained vision in low light. Larger Phase 3 trials were started to follow that up.

The pattern will be familiar by now. A miss on the headline measure, a signal underneath it, and a decision to keep going.

What researchers can take from the elamipretide story

We think there are several practical lessons here for anyone working with elamipretide at the bench.

Time matters

Short exposures have repeatedly shown less than long ones. A few hours or a few days often produced little. Months produced more. If mitochondrial structure needs to be rebuilt and tissue then needs to remodel, that is not surprising. When you design a study, think hard about duration.

The model matters

The clearest results came where cardiolipin is plainly involved. The murkiest came in conditions with many contributing causes. If your model has a clear cardiolipin or inner membrane defect, you are on firmer ground.

Endpoints matter

Several trials missed a functional endpoint while showing a change in a structural or biochemical one. In lab work you have the freedom to measure both. Use it. Do not rely on a single readout.

Safety has been consistent

Across every trial, the main side effect was irritation at the injection site. That is clinical information and not directly relevant to in-vitro work, but it does tell you that the molecule is not broadly toxic to cells at the exposures studied.

There is a lot more detail on mechanism in our article on MTP131 and cardiolipin, and on study design in our piece on Szeto Schiller 31 research models.

Research-grade elamipretide is not Forzinity

We need to be clear about this, because approval has caused some confusion.

The approved product is a sterile pharmaceutical made under drug manufacturing regulations, prescribed by specialists and dispensed to named patients. It has gone through every check that implies.

What we supply is elamipretide as a research chemical. It is the same molecule, made by peptide synthesis, purified, tested by HPLC and mass spectrometry and freeze-dried into vials. It is sold to laboratories for in-vitro research. It is not sterile-filled for injection, it is not a medicine, and it is not for human or animal use. We will not discuss dosing, and we will not sell to anyone who tells us they intend personal use.

If you or someone in your family has Barth syndrome, the right route is a specialist clinic and the approved product, not a research supplier.

Ordering elamipretide for laboratory research

For labs, the practical details are these. We stock elamipretide in four purity grades and in vials from 5 mg to 500 mg.

• Standard Grade, 5 mg, 98 percent or better, for method development.
• High Purity Grade, 10 mg, for routine cell work.
• Ultra-Pure Research Grade, 10 mg, 99.5 percent or better, HPLC and MS verified.
• Bulk Research Grade, 100 mg, for higher volume users.

Our minimum order is 50 units, and you can mix grades and sizes. Go to the SS-31 peptide page, press Order next to the size you want, and fill in the quantity and delivery address. We reply by email with the total, usually the same day. Payment is by Apple Pay, Zelle, Chime, Cash App, USDT or Bitcoin, and every order ships with the Certificate of Analysis for its lot.

If you need help choosing, the SS31 buying guide covers grades and quantities, and you can always ask through the contact page.

The elamipretide timeline at a glance

It is easy to lose the thread across two decades, so here is the sequence in one place. Dates are approximate where the public record is.

• Early 2000s. Elamipretide is made and characterised in the Szeto and Schiller laboratories as SS-31.
• 2004. First major paper describing mitochondrial uptake and protection.
• 2006. A company is formed to develop the Szeto-Schiller compounds.
• Around 2010 to 2012. First human studies, under the code MTP-131 and the brand name Bendavia.
• 2013. Papers show binding to cardiolipin and rapid effects in aged mouse muscle.
• 2016. The heart attack trial reports. Safe, but the main endpoint is missed. The generic name elamipretide comes into general use.
• 2017 to 2020. Heart failure studies. An early signal, then a negative four-week trial.
• 2019. The Phase 3 trial in mitochondrial myopathy misses its endpoints.
• 2020 onward. Long-term follow-up in Barth syndrome shows steady improvement.
• 2021. The regulator declines to review the first application.
• 2022. The Phase 2 eye trial misses its primary endpoints but shows a structural signal.
• 2024. An advisory committee votes narrowly in favour.
• 2025. A further setback in the spring, then accelerated approval of elamipretide for Barth syndrome in September.

Seen like that, the pattern is plain. The science moved quickly in the first ten years. The clinic took the next ten to catch up, and only did so in one small corner.

The part patients played

No account of elamipretide is complete without the families. Barth syndrome is so rare that most doctors never see a case. The patient community is small, well organised and extremely determined.

When the first application was turned away, parents and patients did not accept it quietly. They gave testimony. They described boys who could not climb stairs before treatment and could afterwards. They pointed out, reasonably, that a regulator demanding a large placebo-controlled trial in a disease with a few hundred known patients was asking for something that could not be done.

That pressure did not change the data. It did change how much attention the data received, and it kept the application alive through several rounds. Whatever view one takes of the evidence, it is hard to imagine the approval happening without them.

There is a wider point in this for anyone working on rare conditions. The standard tools of drug evaluation were built for common diseases. Applying them to very small populations forces awkward choices, and the story of elamipretide is now one of the reference cases for how those choices get made.

What is still being tested

Approval for one indication is not the end of the research. Several questions remain open, and they are worth knowing about because they shape what laboratory work is most useful.

Does the benefit in Barth syndrome hold up in the confirmatory study that accelerated approval requires? That is the condition attached to the decision.

Does the subgroup finding in mitochondrial myopathy stand when tested on its own? A trial limited to patients with defects in nuclear genes for mitochondrial DNA maintenance was set up to find out.

Do the larger eye trials confirm the structural signal seen in Phase 2? Dry macular degeneration affects very large numbers of people, so the answer matters well beyond the mitochondrial field.

And underneath all of these: why does elamipretide appear to work in some settings and not in others that look similar? That is a mechanistic question, and it is one that bench researchers are better placed to answer than clinical trialists. Work on membrane structure, on which proteins the molecule sits beside, and on how different tissues handle cardiolipin all feed into it.

If you are choosing a project, that last question is where we would look. There is plenty of room, the tools exist, and elamipretide is easy to obtain.

A practical note for labs

None of the clinical history changes how research-grade elamipretide behaves at the bench. It is the same stable, water-soluble tetrapeptide it was in 2004. What the history does change is the questions worth asking of it, and the standard of evidence a reader will expect. Plan for longer exposures, more than one readout, and a lot-specific certificate on file.

Questions people ask about elamipretide

Is elamipretide the same thing as SS-31?

Yes. SS-31 was the original laboratory name. elamipretide is the official generic name assigned later.

Is elamipretide FDA approved?

A pharmaceutical form received accelerated approval in the United States in September 2025 for Barth syndrome. That approval covers that product for that condition. It does not cover research chemicals.

Why did so many elamipretide trials fail?

Different reasons in different trials. Short treatment periods, mixed patient populations and endpoints that may have been too blunt all played a part. Elamipretide also may simply not help in some conditions.

Where can I read the trial records?

Registered studies are listed on ClinicalTrials.gov, and published papers can be found by searching PubMed.

Do you sell elamipretide for personal use?

No. Research use only, sold to laboratories and institutions.

A last word

It would be easy to tell this as a story of triumph. It is closer to a story of persistence. Most of the trials failed on their main measure. One rare disease, with a direct link to the molecule's target, eventually came good after years of follow-up and a great deal of argument.

For researchers that is not a discouraging picture. It says the biology is real, that it is specific, and that there is a lot still to work out about where and how it applies. That is what research is for. If you are setting up work in this area and need material, the sizes and prices are on the SS-31 peptide page. A general overview of the molecule is also available on Wikipedia.

SS31 peptide purity is the number everybody quotes and hardly anybody checks. Ninety-eight percent. Ninety-nine. Ninety-nine point five. It gets printed on labels and product pages as if it settled the matter. It does not, not on its own, and we say that as people who print those numbers ourselves.

A purity figure only means something if you know how it was measured, on which lot, and what it leaves out. This article walks through six ways to check, starting with the ones that cost nothing and ending with the ones that need an instrument. You do not have to do all six. But you should know what each can and cannot tell you.

What purity means for SS31 peptide, and what it does not

When a supplier says a vial of SS31 peptide is 99 percent pure, they almost always mean one specific thing. A sample was run through an HPLC with a UV detector, and 99 percent of the light absorbed came from one peak. That is it.

This is a useful measurement. It is also narrower than it sounds. Three things it does not tell you:

It does not tell you what the main peak is. A sample could be 99 percent of some other peptide entirely. Purity is not identity.

It does not count things the detector cannot see. Water, salts and counter-ions do not absorb UV at the wavelength used. A vial can be 99 percent pure by HPLC and still be a fifth water and acetate by weight.

It does not tell you how much peptide is in the vial. That is a separate measurement called net peptide content, and most suppliers do not report it unless asked.

None of this is a scandal. It is simply how the measurement works. The trouble comes when a single number is treated as the whole answer.

Where the impurities in SS31 peptide come from

It helps to know what you are looking for. SS31 peptide is made by solid-phase peptide synthesis. The chain is built one amino acid at a time on a resin bead, then cut off and purified.

Each step is very efficient but never perfect. The usual by-products are these.

• Deletion sequences. A coupling step fails on some chains, so you get a three-residue peptide missing one amino acid.
• Truncated sequences. The chain stops growing early.
• Incompletely deprotected peptide. A protecting group that should have come off stays on, most often on the arginine.
• Racemised product. One amino acid flips to its mirror image. With a D-arginine already in the sequence by design, this one needs care to detect.
• Oxidised product. The dimethyltyrosine is electron-rich and can pick up an oxygen.

Because the SS31 peptide is only four residues long, there are fewer steps and fewer chances for these to build up. That is the main reason high purity is realistic for this compound. A good synthesis followed by a good preparative HPLC run will get you past 99 percent without heroics.

Way 1: Read the Certificate of Analysis line by line

This is free and takes five minutes. Every order of SS31 peptide from us ships with a COA, and you can ask for it before you buy.

Go through it like this.

The lot number

Find it. Then find the lot number on your vial. They must match. If the COA has no lot number, it is not a certificate of anything.

The date

A COA should be dated within a sensible time of manufacture. A certificate that is years older than the stock it is supposed to describe deserves a question.

The HPLC result

Look for the purity percentage and the method: column type, mobile phase, gradient, detection wavelength. Peptides are usually read at 214 or 220 nanometres, where the peptide bond absorbs. A chromatogram should be attached or available on request.

The mass spec result

The expected mass for the free base is 639.8. You should see a signal at 640.8 for the singly charged ion, or at 320.9 for the doubly charged one, depending on the instrument. If mass spec is missing, identity has not been confirmed.

Appearance and storage

White to off-white powder. Store at minus 20. If the certificate describes something different from what is in your hand, stop and ask.

Way 2: Learn to read the chromatogram

Most buyers skip the picture and look only at the number. The picture is where the information is.

A chromatogram is a line that runs flat along the bottom and jumps up into peaks. Time runs along the horizontal axis. Each peak is something coming off the column. For a clean lot of SS31 peptide you want to see one tall, narrow, symmetrical peak and very little else.

Things to look for:

• A shoulder on the main peak. This suggests an impurity that almost co-elutes, often a deletion sequence or a racemised form. The purity figure may be flattering.
• A wide, lumpy main peak. Either the column is tired or there is more than one thing under there.
• A baseline that has been cut off just above zero. Zooming the vertical axis out makes small peaks vanish. Ask for the full scale.
• A very short run. If the gradient is over in five minutes, closely related impurities may not have had time to separate.

You do not need to be an analytical chemist to spot these. You only need to have looked at a few good traces so that a bad one stands out. We are happy to talk through the trace for any lot we sell. Write to us through the contact page.

Way 3: Check identity, not only purity

We keep returning to this because it is the gap people fall into. HPLC with a UV detector tells you how many things are in the sample and in what proportion. It does not tell you what they are.

Mass spectrometry does. It weighs the molecules. SS31 peptide has a monoisotopic mass that no common by-product shares, so a clean mass spectrum with the right signal is strong evidence that the main peak is what it should be.

The best arrangement is LC-MS, where the HPLC feeds directly into the mass spectrometer and every peak gets weighed as it comes off. That way you learn not just that there is a one percent impurity but what its mass is, which usually tells you what went wrong in synthesis.

Our Ultra-Pure Research Grade and Bulk Research Grade are verified by both HPLC and mass spectrometry as a matter of course. For the other grades, mass spec data is available on request.

Way 4: Ask about net peptide content and counter-ion

If you are calculating concentrations, this matters more than the difference between 99.0 and 99.5 percent purity.

A freeze-dried peptide is a salt. The positively charged groups on SS31 peptide, and there are three of them, are each paired with a negative counter-ion. After a standard purification that counter-ion is trifluoroacetate. Many suppliers exchange it for acetate or chloride, because TFA can interfere with cell-based assays at high enough concentrations.

Three counter-ions on a molecule this small add up. Three TFA ions weigh 342, against 640 for the SS31 peptide. Add a few percent residual water, and the actual peptide in a vial of TFA salt might be only 60 to 65 percent of the powder weight. For an acetate salt it is higher, roughly 75 to 80 percent.

So ask two things. What is the counter-ion? And is the weight on the label the net peptide or the gross powder? Both ways of labelling are legitimate. You just need to know which you have. Our article on elamipretide peptide chemistry goes further into salt forms and why they matter.

Way 5: Run your own HPLC

If your lab or a core facility down the corridor has an HPLC, use it. Nothing beats your own data, and a supplier who objects to being checked is telling you something.

A basic reverse-phase method is enough.

• Column: C18, analytical scale.
• Mobile phase A: water with 0.1 percent TFA.
• Mobile phase B: acetonitrile with 0.1 percent TFA.
• Gradient: something like 5 to 60 percent B over 20 to 30 minutes.
• Detection: 214 or 220 nanometres.

SS31 peptide is quite polar, so it comes off early. If your gradient starts too high in organic solvent it will shoot through with the solvent front and you will see nothing useful. Start low.

Dissolve a small amount in water, inject, and compare your trace to the one on the COA. Retention times will differ because your system is not the supplier's. What should agree is the overall picture: one dominant peak, and impurities at about the same relative positions and sizes.

If your result is far from the certificate, do not jump to conclusions. Check your column, your sample prep and your integration settings, then contact the supplier with your data. Disagreements are usually about method differences and can be sorted out in a couple of emails.

Way 6: Send a sample for third-party testing

For work that will be audited, or for a large order where a lot depends on the outcome, an independent lab removes any doubt. You send a vial, they run HPLC and mass spec, sometimes amino acid analysis for net peptide content, and they send you a report with their own letterhead on it.

It costs money and takes a week or two. It is not something to do for every order. It makes sense in these situations:

• You are qualifying a new supplier.
• You are about to commit to a long study with a single lot.
• Your institution or a regulator requires independent verification.
• You got a strange result and want to rule the material in or out.

We support this. Third-party lot testing is available on request for our Ultra-Pure grade, and institutional buyers can ask for lot-specific documentation before purchase on bulk orders.

What the grades of SS31 peptide mean in practice

Putting this together with what we actually sell.

Standard Grade is 98 percent or better by HPLC, with a COA for every batch. Up to two percent of the UV-absorbing material is something other than the target. For screening and method work, that is fine.

High Purity Grade tightens the specification and is the one most cell culture labs use day to day.

Ultra-Pure Research Grade is 99.5 percent or better, dual verified, with full batch traceability. Half a percent or less of impurities. This is the grade to buy when the material itself might be questioned.

Bulk Research Grade is 99 percent or better, HPLC and MS verified per production lot, in vials up to 500 mg.

Which to choose is a question about the experiment, not about which number is biggest. We go through that decision in the SS31 buying guide.

Purity changes after the vial leaves us

A certificate describes the material on the day it was tested. What happens after that is up to storage and handling.

Dry SS31 peptide at minus 20 holds its purity very well. The same material left open on a bench, or dissolved and thawed ten times, does not. If you test a vial that has been badly stored and find it below specification, the synthesis is not what failed.

This is worth remembering before raising a complaint, and worth remembering when planning a long project. The eight habits that keep a lot stable are in our SS-31 peptide storage guide.

Red flags when buying SS31 peptide

We see the same warning signs often enough to list them.

• No COA, or a COA only after you have paid.
• One generic certificate for every lot.
• Purity claimed with no method stated.
• No mass spec at all.
• A chromatogram that looks like a screenshot of a screenshot, with unreadable axes.
• Prices far below the rest of the market.
• Health claims or dosing advice on the product page. A real research supplier does not give either.

One of these might be carelessness. Several together are a pattern.

How to order tested SS31 peptide from us

We sell wholesale, from a minimum of 50 units, with no upper limit. You can mix grades and sizes within an order, and other compounds such as BPC-157, GHK-Cu, TB-500 and Retatrutide count toward the minimum.

Press Order next to any size on the SS-31 peptide page. The form opens with that item filled in. Add the number of units, your delivery address and preferred payment method, and if you want to see the COA first, say so in the message. We reply by email, usually the same day, with the total, the payment details and the certificate.

Payment is by Apple Pay, Zelle, Chime, Cash App, USDT or Bitcoin. The order ships with its paperwork.

A worked example: checking one lot of SS31 peptide

Theory is easier with a case in front of you. Imagine a box of fifty 10 mg vials has just arrived, and here is what the certificate says.

Lot number: a string of letters and digits. Date of analysis: last month. Appearance: white lyophilized powder. Purity by HPLC at 220 nm: 99.6 percent. Mass by ESI-MS: found 640.4, expected 640.4 for the singly charged ion. Storage: minus 20.

Step one. Pick up a vial and read its label. Same lot number? Good. If not, stop here and write to the supplier.

Step two. Look at the chromatogram. There is one tall peak at about nine minutes. Either side of it, two or three small bumps, each well under half a percent. The baseline is flat and the scale has not been cropped. The run lasts twenty-five minutes, which is long enough for close relatives to separate. That is what a clean lot of SS31 peptide looks like.

Step three. Check the mass. 640.4 is right for the molecule plus one proton. If the spectrum is attached, you may also see a larger signal near 320.7. That is the same molecule carrying two protons, and it is normal.

Step four. Look for what is not there. This certificate does not state net peptide content or the counter-ion. So you ask. The answer comes back: acetate salt, vials filled by gross weight. Now you know that each 10 mg vial holds roughly 7.5 to 8 mg of SS31 peptide itself, and you can calculate concentrations properly.

Step five, if you have the equipment. Dissolve the contents of one vial, inject, and see whether your trace resembles the supplier's. One dominant peak, small impurities in about the same places. Done.

The whole exercise takes under an hour, most of it the HPLC run, and at the end you know more about that lot than most buyers ever find out.

Amino acid analysis, the test people forget

HPLC and mass spec get the attention. There is a third method worth knowing about, because it answers the question the other two cannot: how much peptide is actually in the powder.

In amino acid analysis, a weighed sample is broken down completely into its individual amino acids with strong acid. Those are then separated and measured. From the amounts recovered, you can work back to how much peptide was in the sample you weighed.

For SS31 peptide there is a wrinkle. Dimethyltyrosine is not a standard amino acid, so it is not in the usual calibration set, and D-arginine reads the same as ordinary arginine in a method that does not distinguish mirror images. In practice the calculation is done from arginine, lysine and phenylalanine, which is perfectly adequate.

You will not get amino acid analysis on every certificate. It is slower and dearer than HPLC. But if net peptide content matters to your work, it is the method to ask for, and an outside lab can run it for you.

Keeping purity records that will survive an audit

If your work may ever be inspected, by a funder, a journal, a quality department or a regulator, what you keep matters as much as what you test.

For each lot of SS31 peptide, hold on to these.

• The supplier's certificate, as received.
• The order confirmation showing grade, size and quantity.
• A photo or note of the vial label with its lot number.
• Your own test results, if you ran any, with the raw data files.
• The dates the lot arrived, was first opened and was used up.
• Which experiments used it.

A folder per lot, paper or electronic, is enough. The aim is that someone who was not there can trace any result back to the material that produced it. It is dull work. It is also the difference between a finding that stands and one that gets a question mark put next to it.

A note on comparing suppliers of SS31 peptide

If you are weighing two sources of SS31 peptide, ask both for the certificate of the lot they would ship today, and put the two side by side. Do not compare the headline purity. Compare the chromatograms, the run lengths, whether mass was confirmed and whether the lot numbers look real. The better SS31 peptide is usually obvious within a minute, and it is not always the one with the bigger number on the label.

Questions about SS31 peptide purity

Is 98 percent SS31 peptide good enough?

For many purposes, yes. It depends on whether two percent of related peptide impurities could affect your readout. For a first look at whether an assay responds, it rarely does.

Why is HPLC purity not the same as the amount in the vial?

Because HPLC only sees what absorbs UV. Water and counter-ions are invisible to it but still have weight. Net peptide content is the figure that accounts for them.

Can you send the COA before I order?

Yes. Ask through the contact form and name the grade and size.

What if my own test disagrees with your COA?

Send us your chromatogram and method. Most differences come down to gradient, column or integration, and we can usually work out which. If the material is at fault, we put it right.

Does higher purity SS31 peptide work better?

Not in the sense of being stronger. It contains less of other things. Whether that matters depends on how sensitive your experiment is to those other things.

Bottom line

A purity number is a starting point. Check the lot number. Look at the trace, not just the figure. Make sure identity was confirmed by mass. Ask about counter-ion and net content. Test it yourself if you can. Use an outside lab when the stakes justify it.

For a general introduction to the compound, see our essential facts about SS-31. When you are ready to order, the grades and prices are on the SS-31 peptide page.

SS-31 peptide is one of the more forgiving compounds to keep in a lab. It is short, it has no cysteine or methionine to oxidise, and it does not clump the way long sticky peptides do. Even so, we hear from people every month whose results went sideways, and when we dig into it the cause is nearly always storage or handling, not the material.

So here are the eight rules we follow ourselves. They are not complicated. Most take no extra time once they are habit. A couple of them will feel fussy until the day they save an experiment.

Why SS-31 peptide comes as a powder in the first place

Every vial of SS-31 peptide we ship is lyophilized, which is the technical word for freeze-dried. The SS-31 peptide is dissolved, frozen, and then the ice is pulled off under vacuum without ever becoming liquid water again. What is left is a dry cake or a loose powder at the bottom of the vial.

The point of doing this is stability. Nearly everything that damages a peptide needs water to happen. Hydrolysis needs water. Bacterial growth needs water. Most oxidation runs faster in solution. Take the water away and the clock all but stops.

That is why a dry vial can cross an ocean in a padded envelope and arrive fine, while the same peptide in solution would need dry ice and a prayer. It is also why the first rule is what it is.

Rule 1: Keep SS-31 peptide dry until you need it

Do not reconstitute a vial because it has arrived and you feel like getting organised. Leave it sealed. Powder keeps for a long time. Solution keeps for days to weeks.

If your study runs for three months and uses one vial a week, twelve vials stay in the freezer untouched and one gets opened each Monday. It sounds too simple to be worth writing down. It is the single most common thing people get wrong.

Rule 2: Minus 20 for the long term, and pick the freezer carefully

For anything longer than a few weeks, store dry SS-31 peptide at minus 20 degrees Celsius. Minus 80 is fine too if you have the space, but it is not necessary for this compound.

The type of freezer matters more than most people expect. Household style frost-free freezers stay frost-free by warming up several times a day to melt the ice off the coils. Your samples go through that cycle with them. A manual defrost laboratory freezer holds a steadier temperature. If frost-free is all you have, put the vials in an insulated box at the back, away from the door, so they are buffered from the swings.

For short periods, a few days to a couple of weeks, a sealed dry vial in the fridge at 2 to 8 degrees is acceptable. Room temperature for the length of a delivery is also fine. What you want to avoid is months on a shelf.

Rule 3: Keep light and moisture out

The dimethyltyrosine residue in SS-31 peptide is the chemically active part of the molecule. It is also the part most likely to react if you give it the chance. Light and oxygen both help that along.

In practice this means keeping vials in their box or in an opaque container, and not leaving them on a sunny bench while you set up. It is not a compound that falls apart in ten minutes of daylight. But there is no reason to test that.

Moisture is the bigger risk. A freeze-dried powder is hygroscopic, which means it pulls water out of the air. Once a vial has been opened, it will never be as dry again. If you must store an opened vial of powder, cap it tightly, wrap the cap with film, and put it in a container with desiccant.

Rule 4: Warm the vial before you open it

This is the fussy one. Take a vial straight from minus 20, pop the cap, and the cold glass and cold powder will condense water out of the room air within seconds. You cannot see it happen. You have just added water to your dry peptide, and if you then put the vial back in the freezer, that water goes with it.

The fix costs nothing. Take the vial out, leave it sealed on the bench for twenty to thirty minutes until it reaches room temperature, then open it. If you are in a humid climate, give it a little longer or let it warm inside a desiccator.

We would guess that half of all reports of a peptide that went off in storage trace back to skipping this step.

Rule 5: Choose the solvent for the experiment, not from habit

SS-31 peptide dissolves easily in water. With three positive charges at neutral pH, it is about as water-soluble as peptides get. You do not need DMSO, you do not need acetic acid, and you do not need to sonicate it.

What you dissolve it in should depend on where it is going next.

• For cell culture, sterile water or a simple buffer such as PBS, then dilute into medium.
• For analytical work, HPLC-grade water, or water with a little acetonitrile if that suits your method.
• For isolated mitochondria, whatever respiration buffer the assay calls for.

Make a concentrated stock rather than dissolving straight to the final working concentration. A stock of a few milligrams per millilitre is easy to pipette accurately and can be diluted to anything you need. Very dilute peptide solutions lose material to the walls of the tube, and you will not know how much.

When you add the solvent, run it gently down the inside wall of the vial instead of squirting it onto the powder. Then swirl. Do not shake hard and do not vortex for a minute straight. This peptide is tough enough to take it, but it is a good habit for every peptide, and habits should not depend on remembering which compound is in your hand.

Rule 6: Aliquot on day one

Once SS-31 peptide is in solution, the enemy is the freeze-thaw cycle. Each time a solution freezes, ice crystals form and the SS-31 peptide gets concentrated into the shrinking pockets of liquid between them. Each time it thaws, the reverse happens. Do that five or six times and you can measure the loss.

The answer is to split the stock into single-use portions the day you make it. Work out how much you use in one session, pipette that amount into a row of small tubes, label them, and freeze them all. Each tube is thawed once, used, and whatever is left is thrown away.

A few practical notes from doing this more times than we can count:

• Use low-binding polypropylene tubes. Ordinary tubes work, but low-bind tubes lose less.
• Label before you fill. Cold wet tubes do not take ink.
• Write the concentration, the date and the lot number. Not just the name.
• Freeze the tubes quickly. A metal block that has been sitting in the freezer does the job.

It adds fifteen minutes on day one. It removes a variable from every experiment after that.

Rule 7: Respect the clock on solutions

How long does SS-31 peptide last in solution? The honest answer is that it depends on the solvent, the concentration, the temperature and how clean your technique was. The Certificate of Analysis that ships with your order gives a timeframe for the lot, and that is the figure to go by.

As general guidance, a sterile stock kept at 2 to 8 degrees is something to use in days to a couple of weeks, not months. Frozen aliquots last much longer. Anything left at room temperature overnight should be treated with suspicion.

Contamination is the other half of this. A peptide solution is food for bacteria. If your stock goes cloudy, or develops anything floating in it, bin it. Do not filter it and carry on. Sterile technique when you reconstitute, and sterile-filtered solvent, prevent most of this.

Rule 8: Write it down

When something goes wrong three months into a project, the first thing you will want to know is which lot was in use, when it was reconstituted, and how many times that tube had been thawed. If none of that is written anywhere, you are guessing.

Keep a simple log. Date received. Lot number. Date reconstituted. Solvent and concentration. Number of aliquots made. It can be a page taped inside the freezer door. Staple the COA to it.

This is also what makes a re-order straightforward. When you can tell us exactly which lot you had and how it behaved, we can tell you whether the same lot is still available.

What degraded SS-31 peptide looks like

Usually it looks like nothing. That is the problem. A solution that has lost a fifth of its activity looks the same as a fresh one.

There are a few visible signs worth knowing. Powder that has gone sticky, glassy or yellowish has picked up moisture. A solution that is cloudy or has particles is contaminated or has come out of solution. A vial whose cake has collapsed into a film on the glass may simply have been warmed in transit, which is harmless, or may have been wet, which is not. If you are not sure, send us a photo.

The reliable test is analytical. If you have access to an HPLC, run a sample and compare the trace to the one on the COA. New peaks, or a main peak that has shrunk, tell you what your eyes cannot. We explain how to read those traces in our piece on SS31 peptide purity testing.

How our SS-31 peptide is packed and shipped

Knowing how it left us helps you judge how it arrived.

Each vial is sealed under a crimped cap and labelled with the compound, grade, fill and lot number. Vials are packed to stop them knocking together and shipped with the Certificate of Analysis for the lot. Because the powder is dry, transit at ambient temperature is not a concern over normal delivery times.

When the box arrives, check three things before it goes in the freezer. The seal on each vial is intact. The lot number on the vials matches the COA. The count is right. If anything is off, photograph it and write to us through the contact page the same day.

Which vial size makes storage easiest

This is a question that should come up at ordering time and often does not.

Small vials, such as the 5 mg Standard Grade or the 10 mg High Purity, suit labs that use a little at a time. One vial, one batch of aliquots, no opened powder going back into storage.

Larger vials, such as the 50 mg Ultra-Pure or the 100 mg Bulk, are cheaper per milligram but only make sense if you will reconstitute and aliquot the whole thing in one go. Opening a 500 mg vial, weighing out a little and resealing it, week after week, is the worst way to store any peptide.

If you are unsure which pattern fits, tell us how much you use per week when you enquire and we will suggest a mix. There is more on choosing sizes in our SS31 buying guide.

Storage for the other peptides we carry

The same rules apply, with small differences. BPC-157 is also stable and water-soluble. TB-500 is longer and benefits even more from gentle handling and low-bind tubes. GHK-Cu is a copper complex and its solutions are blue, which surprises people the first time. Retatrutide carries a fatty acid chain and can be slower to dissolve, so give it time and do not shake it.

Dry at minus 20, warm before opening, aliquot on day one. That covers all five.

A day-one routine for a new box of SS-31 peptide

Rules are easier to follow as a sequence. Here is what we would do, in order, on the day a box of SS-31 peptide lands on the bench.

• Open the box and count the vials against the packing list.
• Compare the lot number on a vial with the lot number on the Certificate of Analysis.
• Check each seal. Set aside anything cracked or loose and photograph it.
• Write the arrival date and lot number in the freezer log.
• Put all but the vials you need this week straight into the minus 20, in their box, at the back.
• Leave the working vial sealed on the bench for half an hour.
• While it warms, label your aliquot tubes and get the solvent ready.
• Open the vial, add solvent down the wall, swirl until clear.
• Pipette the stock into the labelled tubes, cap, and freeze.
• Note the reconstitution date, solvent, concentration and number of tubes in the log.

That is forty-five minutes, most of it waiting. After that, every experiment starts from a fresh, single-use tube of SS-31 peptide at a known concentration, and you never have to think about it again.

When the freezer fails

It happens to every lab eventually. A compressor dies over a long weekend, or someone leaves a door ajar, and you come in to a puddle.

For dry, sealed SS-31 peptide, a freezer failure is rarely a disaster. The powder tolerates room temperature for days. Move the vials to a working freezer, make a note of roughly how long they were warm, and carry on. If the outside of the vials got wet from meltwater, dry them and check that the labels are still readable.

Frozen aliquots are a different matter. If they thawed and sat at room temperature for more than a few hours, we would discard them and make fresh ones from a new vial. It is not worth building weeks of work on a stock you are unsure about. If they thawed but stayed cold, in a freezer that had only drifted up to fridge temperature, they are probably usable for non-critical work, and you should run a check before relying on them.

Two cheap precautions make this much less painful. A temperature logger or alarm on the freezer. And spare sealed vials held back, so that losing your aliquots costs you an afternoon and not a month.

Moving SS-31 peptide between sites

Labs relocate, and people carry samples to collaborators. A few points.

Move it dry if you possibly can. Sealed vials of powder can travel in a padded box at ambient temperature with no special arrangements. That is how they reached you in the first place.

If you must move solutions, send them frozen on dry ice by a courier that handles it properly, and treat each tube as having used up its one thaw when it arrives.

Send the paperwork with the material. A copy of the certificate and a note of the lot number, the reconstitution date and the concentration should travel in the same box. A tube labelled only with a name and a date is close to useless to the person receiving it.

And do not carry research chemicals in hand luggage across a border on the assumption that nobody will ask. Use a courier and proper documents.

Does grade change how you store it?

No. Standard, High Purity, Ultra-Pure and Bulk are all the same molecule and all behave the same way in storage. What changes is how much it matters if you get it wrong. A slip with a pilot vial costs you a few dollars. A slip with the single lot of SS-31 peptide set aside for a year-long study costs a great deal more. Store everything as if it were the expensive one, and the habit will be there when it counts.

The one-line version for the freezer door

If you want something to tape up where people will see it, use this. Dry SS-31 peptide lives at minus 20. Let the SS-31 peptide vial warm before opening. Dissolve SS-31 peptide in water, aliquot at once, thaw each tube only once. Log the lot. Four lines cover nearly everything that goes wrong with SS-31 peptide in a shared lab, and new students will actually read four lines.

Questions we get about storing SS-31 peptide

My SS-31 peptide sat at room temperature for a week in customs. Is it ruined?

Almost certainly not, provided the vial stayed sealed. Dry SS-31 peptide is stable at ambient temperature for that kind of period. Put it in the freezer now and carry on.

Can I store reconstituted SS-31 peptide at minus 20?

Yes, as single-use aliquots. Do not freeze a whole stock and thaw it each time you need some.

Does the vial need to be under nitrogen or argon?

Not for routine work. If you are storing opened powder for a long time, flushing the vial with inert gas before recapping does no harm.

How much liquid should I add?

That depends on the stock concentration you want. Divide the milligrams in the vial by the millilitres you add. Check with your supplier whether the stated fill is net peptide or gross powder, because it changes the sum. Our article on elamipretide peptide chemistry explains why.

There is hardly any powder in my vial. Is it under-filled?

Five milligrams of freeze-dried peptide is a very small amount to look at, and it often sits as a thin film. That is normal. The fill is by weight, not by appearance.

To sum up

Keep it dry. Keep it cold. Keep it dark. Warm the vial before opening. Dissolve in water or simple buffer. Aliquot the same day. Use solutions promptly. Write everything down.

Do those eight things and SS-31 peptide will behave the same in month six as it did in week one. If you are setting up a new project and want to order, current sizes and prices are on the SS-31 peptide page. Our minimum is 50 units, we reply to most enquiries the same day, and every order ships with its COA. For background on the compound itself, see our essential facts about SS-31, and for more on how peptides are freeze-dried there is a good general overview on Wikipedia.

SS31 is not hard to buy. It is hard to buy well. There are dozens of sellers, the prices are all over the place, and from the outside one white powder in a glass vial looks exactly like another. We have been on both sides of this, as buyers before we were sellers, and most of what follows is stuff we learned by getting it wrong first.

This guide is written for someone placing a real order: a lab manager, a purchasing officer, a reseller, or a researcher who has been handed the job because nobody else wanted it. Seven checks. None of them takes long.

First, a note on the name SS31

You will see it written SS31, SS-31, SS 31 and occasionally ss31 in lower case. It is all the same compound. The hyphenated form is the one used in the original papers. The version without the hyphen took over online because people type it that way into search boxes and order forms. Elamipretide and MTP-131 are also the same molecule under official and company names.

Why does this matter for buying? Because a supplier who lists SS31 and elamipretide as two different products at two different prices either does not know what they are selling or hopes you do not. Either way, move on.

Check 1: Decide what the SS31 is for before you look at prices

This sounds obvious and almost nobody does it. People open a price list, see that the top grade is three times the cost of the bottom one, and pick the middle out of instinct.

Start from the experiment instead. Ask what happens if there is one percent of something else in the vial. For a pilot study where you are only trying to find out whether your cells respond at all, the answer is usually nothing. For a dose-response curve that will end up as a figure in a paper, the answer may be quite a lot. For analytical work where SS31 itself is the reference standard, impurities are the whole problem.

Write down the answer in one sentence. Then look at the price list. You will choose differently.

Check 2: Match the SS31 grade to the job

We carry four grades. Here is how we would steer a colleague.

Standard Grade

Standard Grade is stated at 98 percent purity or better, verified by HPLC. Use it for method development, for training new staff, for checking that a protocol works before you commit expensive material. It is also a sensible choice for teaching labs. Sizes run from 5 mg to 50 mg.

High Purity Grade

High Purity Grade is the workhorse. If you run cell culture experiments week in, week out, this is probably where you will land. It costs a little more than Standard and gives you a tighter specification. Same size range.

Ultra-Pure Research Grade

Ultra-Pure Research Grade is 99.5 percent or better, with identity confirmed by mass spectrometry as well as purity by HPLC, and third-party lot testing available if you ask. This is for work that will be scrutinised. If a reviewer or an auditor is going to want to see what was in the vial, buy this and keep the COA with your records. The 50 mg vial is the most economical way into this grade.

Bulk Research Grade

Bulk Research Grade is 99 percent or better and comes in 100 mg, 250 mg and 500 mg vials. It exists for groups that would otherwise be opening ten small vials a week. Per milligram it is the cheapest way to buy SS31 from us by a wide margin.

A mistake we see often: buying Ultra-Pure for everything because it feels safer. It is not safer, it is just dearer. Put the money where it changes the result.

Check 3: Work out how much SS31 you really need

People under-order, then re-order from a different lot, then spend a week wondering why the second half of the study looks different from the first. Lot-to-lot variation in a well made peptide is small, but it is never zero, and it is one more variable you did not need.

A rough way to size an order:

• Work out the amount per experiment from your protocol.
• Multiply by the number of experiments, including repeats.
• Add a third for the runs that fail, because some will.
• Round up to a quantity that comes from a single lot.

Then ask the supplier to fill the whole order from one lot. We do that by default where stock allows, and we tell you if we cannot.

Vial size matters as well. Fifty 5 mg vials and five 50 mg vials contain the same amount of SS31, but they behave very differently in a working lab. Small vials mean each one is opened once and used up, which is kinder to the peptide. Large vials are cheaper per milligram and a nuisance unless you split them into portions on day one. Choose based on how your bench actually works, not on the unit price alone.

Check 4: Read the Certificate of Analysis properly

The COA is the only evidence you have that the vial contains what the label says. Treat it like evidence.

A real COA for SS31 should show these things.

• A lot or batch number that matches the number on your vials.
• The date of analysis.
• Purity by HPLC, as a percentage, ideally with the chromatogram.
• Identity by mass spectrometry, showing a mass consistent with 639.8 g/mol.
• Appearance, which should be a white to off-white powder.
• Storage conditions.

Now the things that should make you suspicious. A COA with no lot number. A COA dated two years ago for material you are told is fresh. A purity figure with no method next to it. A mass spec result that is missing entirely. And the classic: the same PDF sent to every customer no matter which lot they receive.

If you have never read a chromatogram, it is less scary than it looks. One tall peak is your compound. Small peaks either side are impurities. The purity figure is the area of the tall peak divided by the area of everything. We go through an example step by step in our article on SS31 peptide purity testing.

Check 5: Ask what the stated weight means

This one catches experienced buyers. When a vial says 10 mg, does that mean 10 mg of SS31, or 10 mg of powder?

They are not the same. A freeze-dried peptide is never pure peptide. It carries counter-ions left over from purification, usually acetate or trifluoroacetate, and a little residual water. In a small, highly charged peptide like this one, those extras can make up a meaningful share of the powder weight. The actual peptide content might be 75 to 90 percent of what the balance reads.

Neither way of labelling is dishonest as long as the supplier tells you which they use. But if you are calculating molar concentrations, you need to know. Ask. A supplier who understands the question is a supplier who understands their product. If you want the chemistry behind it, our piece on elamipretide peptide chemistry covers salt forms in more detail.

Check 6: Look at how the supplier handles the boring parts

Purity gets all the attention. Logistics is where orders actually go wrong.

Packaging. Vials should arrive sealed, with crimped caps, labelled with compound name and lot number. Loose labels and handwritten lot numbers are a bad sign.

Shipping. Freeze-dried SS31 tolerates a few days at ambient temperature without trouble, so cold packs are a nice touch but not a requirement. What matters more is that the parcel is tracked and that somebody answers when you ask where it is.

Communication. Send a question before you order and see how long the reply takes and whether it answers what you asked. That is a preview of what happens when something goes wrong.

Paperwork. If your institution needs an invoice in a particular format, a quote on letterhead or a document for customs, raise it at the start. We deal with these requests all the time through the contact page, and it is far easier to sort out before the order ships than after.

Check 7: Be honest about what a low price means

Making a clean tetrapeptide is not expensive compared with a long, modified one. That is why SS31 costs less per milligram than something like retatrutide. But there is still a floor. Synthesis, purification, two kinds of analysis, freeze-drying, vialling and shipping all cost money.

When a price sits far below everyone else, something has been left out. Usually it is the analysis. Sometimes it is the purification. Occasionally the vial simply contains less than the label says. You will not find out which from the product page.

We are not the cheapest and we do not try to be. Our prices are listed openly on the SS-31 peptide page, from $39 for a 5 mg Standard Grade vial upward, so you can compare without having to ask for a quote first.

How wholesale SS31 orders work with us

Our minimum order is 50 units. There is no maximum. A unit is one vial, and you can ask for any quantity above the minimum.

Here is the whole process.

• Pick a grade and size on the product page and press Order. The enquiry form opens with your choice already filled in.
• Enter the number of units, your delivery address and the payment method you prefer.
• We email back with availability, the total and payment details. Usually the same day.
• You pay by Apple Pay, Zelle, Chime, Cash App, USDT or Bitcoin.
• The order ships with the Certificate of Analysis for its lot.

If you want to split an order across grades or sizes, put that in the message box. Mixed orders are fine. If you need the COA before you commit, ask for it in the same message and we will send it with the quote.

Resellers sometimes ask about repeat supply. Yes, we can set up a standing arrangement, and yes, we can hold a lot for you if you tell us roughly what you expect to need. Write to us and we will work it out.

What about the other peptides

A lot of SS31 orders arrive with something else attached. The most common additions are BPC-157 and TB-500, which tend to be ordered together by groups working on repair models. GHK-Cu goes to cosmetic science and skin biology labs. Retatrutide is the newest and the one with the fastest growing demand.

All of them count toward the 50 unit minimum, so a mixed order of, say, thirty vials of one compound and twenty of another is fine. The same testing and paperwork apply across the board.

Mistakes we see again and again

A short list, because we would rather you learned from other people's orders than your own.

• Ordering the top grade for a pilot study. Covered above. It is the most common waste of money we see.
• Splitting an order across two suppliers to save a little. You now have two lots, two COAs and no way to tell which caused the odd result.
• Not checking the lot number on arrival. It takes ten seconds to compare the vial label with the COA. Do it before the box goes in the freezer.
• Storing vials in a frost-free freezer door. The temperature swings every time the door opens and every time the defrost cycle runs. Put them at the back of a proper minus 20.
• Reconstituting everything on day one. Only dissolve what you will use. Powder keeps. Solution does not. The details are in our SS-31 peptide storage guide.

Working out the real cost of an SS31 order

The price on the page is not the whole cost. When you compare quotes for SS31, put these on the same sheet.

The unit price, obviously. Then shipping, which for a small box of vials is modest but not zero. Then any import duty or handling fee your country applies to laboratory chemicals. Then the cost of the testing you will do on arrival, if any. And finally the cost of failure: what a wasted month of experiments is worth if the material turns out to be wrong.

That last one is never on an invoice. It is still the biggest number on the sheet. A lot of SS31 that costs fifteen percent more and comes with a real, lot-specific certificate is cheaper than a bargain that leaves you guessing.

A practical example. Fifty 10 mg vials of High Purity SS31 at $79 each comes to $3,950. The same fifty vials in Ultra-Pure at $99 comes to $4,950. The difference is a thousand dollars. If the work is a pilot, keep the thousand. If the work is going into a regulatory file, a thousand dollars is trivial next to the cost of repeating it.

International orders and customs

We ship SS31 to buyers in many countries, and the questions are always the same.

Will it clear customs? In most places, a research peptide addressed to a laboratory or company, with a proper commercial invoice describing it as a laboratory reagent for research use, clears without trouble. Rules do differ, and it is the buyer's job to know the local position. If your country needs an import permit for research chemicals, get it before you order.

How should it be described on the paperwork? Accurately. Synthetic peptide, lyophilized, for laboratory research use only, with the CAS number 736992-21-5. We do not mislabel parcels and we will not be asked to.

What if it is held up? Dry SS31 is stable at ambient temperature for the length of any normal delay. A week in a customs shed does it no harm as long as the vials stay sealed. Tell us if a parcel stalls and we will chase the carrier from our end.

Do you need a business address? It helps. Deliveries to a named institution or company go more smoothly than deliveries to a private house, and some carriers will ask.

Planning repeat SS31 orders

If you expect to order more than once, a little planning saves money and trouble.

Tell us your likely usage over the next six to twelve months. With that, we can set aside enough of a single lot to cover you, so that your third order matches your first. This matters most for long studies, where a change of lot halfway through is the last thing you want.

Order before you run out. It sounds obvious. We still get messages on a Friday afternoon from labs that used their last vial on Thursday. Keep a reorder point, say a month of stock, and write to us when you reach it.

Keep the paperwork together. Each order of SS31 comes with its own certificate. File them by lot number alongside your experiment records. When someone asks, two years from now, what was in the vials used for figure three, you will be able to answer in a minute.

Ask about mixed orders. If you also use other compounds from our catalogue, combining them into one shipment cuts the freight cost and counts toward the 50 unit minimum. Many of our regular customers settle into a pattern of one mixed box every couple of months.

And tell us when something was not right. A late parcel, a damaged vial, a certificate that was hard to read. We would much rather hear it and fix it than lose a customer who never said why.

A last check before you send the SS31 order

Read your enquiry back once before pressing send. Is the grade named? The vial size? The number of units? The delivery address complete, with a phone number for the courier? Have you said whether you want SS31 from a single lot, and whether you need the certificate first? Five lines, and it saves a round of emails. Orders with all of that in them usually get a full quote for SS31 back the same day.

Questions buyers ask us about SS31

Is SS31 legal to buy?

It is sold as a research chemical for laboratory use. Rules differ between countries, and it is the buyer's responsibility to know what applies locally. We sell to researchers, laboratories and institutions on the condition that it is for research only.

Is this the same as the approved medicine?

No. A pharmaceutical form of elamipretide received accelerated approval in the United States in 2025 for Barth syndrome. Our material is a research chemical, not that product. It is not for human or animal use. Background on the molecule is on Wikipedia.

Can I get a sample before a large order?

Ask. We look at it case by case, and it helps if you tell us what you plan to test.

How do I know the SS31 I receive matches the COA?

The lot number on the vial matches the lot number on the certificate. If you have access to an HPLC, run it yourself. We would encourage that. A supplier who is confident in their material has no reason to mind.

What if something arrives damaged?

Photograph it before you open anything else and write to us the same day. We sort it out.

The short version

Decide what the SS31 is for. Pick the lowest grade that does the job. Order enough from one lot. Read the COA and check the lot number. Ask whether the weight is net or gross. Test the supplier with a question before you send money. And be wary of any price that looks too good.

If you would like a quote, the quickest route is the Order button on the SS-31 peptide page, or write to us directly through the contact form. For a broader introduction to SS31 itself, start with our nine essential facts about SS-31.

SS-31 is the compound we get asked about more than everything else in our catalogue put together. Some of the people asking have read every paper going. Others saw the name once in a forum thread and want to know what it actually is before they spend money. This article is for the second group, though the first might still find a thing or two worth checking.

We sell SS-31, so we are not neutral. What we can do is tell you what we know from handling it, shipping it and answering the same questions week after week. Nine facts, in the order people usually need them.

1. SS-31 is a four amino acid peptide, and that is unusually small

Most peptides people order for research run from ten to forty amino acids. SS-31 has four. Its sequence is D-Arg-Dmt-Lys-Phe-NH2, which gives it a molecular weight of about 639.8 g/mol. You could draw the whole thing on a napkin.

Two of those four residues are not standard. The first is D-arginine, the mirror image of the arginine your cells normally use. The second is Dmt, short for 2,6-dimethyl-L-tyrosine, which is tyrosine with two extra methyl groups bolted on. Neither was chosen by accident. D-amino acids are hard for enzymes to chew through, so the peptide survives longer. The dimethyltyrosine is what gives the molecule its ability to mop up reactive oxygen species.

Small size matters for practical reasons too. A short peptide is easier to make cleanly, easier to purify and easier to verify. When a supplier says their SS-31 is 99 percent pure, that claim is far more believable for a tetrapeptide than for a 40 residue chain with a fatty acid hanging off it.

2. The name comes from the two people who made it

The SS stands for Szeto and Schiller. Hazel Szeto was a pharmacologist at Weill Cornell in New York. Peter Schiller ran a peptide chemistry lab in Montreal. In the late 1990s and early 2000s they were working on opioid peptides, trying to build better painkillers, and they noticed that some of their compounds were ending up inside mitochondria. That was not supposed to happen. Charged peptides are not meant to walk through cell membranes.

They followed the odd result instead of ignoring it. What came out was a small family of numbered compounds. The number 31 is simply where this one sat in the series. There is no deeper meaning to it. We wrote more about the rest of the family in our piece on the Szeto-Schiller peptide group if you want the longer story.

You will see SS-31 under other names. Elamipretide is the official generic name. MTP-131 was a company code. Bendavia was an early brand name that was later dropped. They all refer to the same molecule. If you are searching the literature, you need all of them, because papers from different years use different labels and the search engines do not always connect them.

3. It goes to the mitochondria without needing a push

This is the property that made people sit up. Most compounds designed to reach mitochondria, such as MitoQ, hitch a ride on the electrical charge across the inner mitochondrial membrane. That works well in healthy cells. It works badly in damaged ones, because damaged mitochondria lose that charge, and those are exactly the mitochondria researchers tend to care about.

SS-31 does not rely on membrane potential in the same way. Its alternating pattern of aromatic and positively charged residues lets it slip across the cell membrane and settle on the inner mitochondrial membrane. Early studies reported it concentrating there a thousand fold or more compared with the surrounding fluid. It gets in fast as well, within minutes in cell culture.

For anyone designing an experiment, the upshot is simple. You do not need a delivery vehicle, a transfection reagent or a carrier. You add it to the medium.

4. What SS-31 actually does once it gets there

For years the short answer was that it is an antioxidant. That turned out to be only part of the picture, and probably not the most important part.

The current view is that SS-31 binds to cardiolipin, a phospholipid found almost only in the inner mitochondrial membrane. Cardiolipin is not a passive bit of fat. It holds the folds of the membrane in shape and helps the protein complexes of the electron transport chain sit together properly. When cardiolipin is damaged or oxidised, those complexes drift, electrons leak and energy production drops.

By sitting on cardiolipin, SS-31 seems to protect it and to keep the membrane organised. A 2013 paper from the Szeto lab showed the interaction directly and linked it to better energy output in stressed mitochondria. Later work using cross-linking found the peptide near a number of the proteins involved in making ATP.

We would be careful with any stronger claim than that. The mechanism is still being argued over. What is not in dispute is that the cardiolipin interaction is real and that it is the starting point for nearly every current study.

5. There is a large body of published research on SS-31

If you search PubMed for the peptide, you will get hundreds of results. Not many compounds sold as research peptides can say that. The work falls into a few broad groups.

• Heart and kidney models, especially injury caused by cutting off and then restoring blood flow.
• Skeletal muscle in ageing animals, where a well known 2013 study in mice reported improved mitochondrial energetics after a single treatment.
• Eye models, including work on retinal cells.
• Inherited mitochondrial conditions, most notably Barth syndrome, which is caused by a fault in cardiolipin processing.
• Neurological models, a smaller and more recent area.

Most of this is preclinical, meaning cells and animals. Some of it went on to human trials run by the company that licensed the molecule. We covered that history, including the trials that failed, in our article on elamipretide. It is worth reading if you want a sober view, because the story is not one long success.

6. The material sold for research is not a medicine

This needs saying plainly. In September 2025 the US Food and Drug Administration granted accelerated approval to a pharmaceutical form of elamipretide for Barth syndrome. You can read the FDA trial snapshot for the details. That product is made under pharmaceutical manufacturing rules, prescribed by doctors and supplied through pharmacies.

The SS-31 we sell is a research chemical. Same molecule, different purpose and different regulatory status. It is sold for laboratory and in-vitro work only. It is not for human or animal consumption, and we do not answer questions about dosing or personal use. If that is what you are after, we are the wrong shop, and so is every other research supplier.

We say this early because it saves everyone time.

7. Purity grades exist for a reason

We stock SS-31 in four grades. People sometimes assume that is marketing. It is not. Different experiments need different things, and paying for purity you will not use is a waste of a grant.

• Standard Grade is 98 percent or better. Fine for method development, practice runs and work where you are checking that an assay behaves at all.
• High Purity Grade is the one most labs settle on for routine cell work.
• Ultra-Pure Research Grade is 99.5 percent or better, verified by both HPLC and mass spectrometry. This is for studies where a reviewer will ask what was in the vial.
• Bulk Research Grade comes in 100 mg, 250 mg and 500 mg vials for groups that go through a lot.

If you are unsure, start one grade lower than you think you need and run a pilot. You can always step up. We have a longer guide to choosing between them in the SS31 buying guide.

8. How SS-31 is tested, and what to ask any supplier

Every lot of SS-31 we ship is checked two ways. HPLC tells you how much of the sample is the main compound and how much is something else. Mass spectrometry tells you whether the main compound has the right molecular weight. You need both. A sample can be 99 percent pure and still be 99 percent of the wrong thing.

The results go on a Certificate of Analysis, which ships with the order. A proper COA has a lot number, a date, the method used and the actual chromatogram or at least the numbers from it. A COA with no lot number is a brochure.

Questions worth asking any supplier, us included:

• Is the COA for the lot I am receiving, or a generic one?
• Was identity confirmed by mass spec, or only purity by HPLC?
• What is the counter-ion, and is the stated weight the peptide content or the gross weight?
• Can I see the COA before I pay?

We answer yes to the last one. Ask through the contact page and name the grade you are interested in. For more on reading the document itself, see our piece on SS31 peptide purity testing.

9. Storage is simple, but people still get it wrong

SS-31 ships as a freeze-dried powder in a sealed vial. In that form it is stable. Keep it at minus 20 degrees Celsius, in the dark, and it will sit happily for a long time. Short trips at room temperature during shipping do not hurt it.

The trouble starts once you add liquid. A peptide in solution is on a clock. Keep it in the fridge at 2 to 8 degrees, use it within the window on your COA and do not freeze and thaw the same tube again and again. If you need to use it over weeks, split it into small portions on day one and freeze those, so each portion is only thawed once.

The other common mistake is opening a cold vial straight from the freezer. Water from the air condenses on the powder. Let the vial come up to room temperature first, then open it. It takes twenty minutes and saves a lot of grief. The full routine is in our SS-31 peptide storage guide.

How ordering SS-31 from us works

We are a wholesale supplier. The minimum order is 50 units, and there is no upper limit. That suits labs with ongoing projects, institutions buying for several groups and resellers.

The process is short.

• Go to the main SS-31 peptide page and look at the sizes and prices.
• Press Order next to the one you want. The enquiry form opens with that item filled in.
• Add the number of units and your delivery address, and pick how you would like to pay.
• We reply by email with the total and payment details.

We accept Apple Pay, Zelle, Chime, Cash App, USDT and Bitcoin. Once payment clears, the order goes out with its COA. Most enquiries get a reply the same day, and we try hard to keep it that way, because we know a stalled order can stall a whole project.

If you need something we do not list, such as a different vial size or a mixed order across grades, just say so in the message. We would rather have that conversation than have you guess.

A few things SS-31 is often confused with

Because it gets discussed alongside other popular research compounds, SS-31 is sometimes lumped in with peptides that work in completely different ways. A quick sort-out.

BPC-157 is a 15 amino acid peptide studied mostly in tissue repair models. It has nothing to do with mitochondria. TB-500 is synthetic thymosin beta-4, an actin-binding peptide studied in cell migration. GHK-Cu is a copper-binding tripeptide from the skin and matrix biology world. Retatrutide is a much larger metabolic peptide that acts on three hormone receptors.

None of those is a substitute for SS-31, and it is not a substitute for any of them. If a study design calls for a mitochondria-targeted compound, this is the one in our catalogue that fits. We stock the other four because labs that order one often need another, not because they are interchangeable.

What we would tell a colleague

If a friend running a lab asked us whether SS-31 was worth looking at, we would say this. It is one of the better characterised research peptides you can buy. The mechanism is interesting and still open enough to be worth studying. The molecule is small and stable, which makes it forgiving to work with. And the literature is deep enough that you will not be working blind.

We would also say: read the negative trials as well as the positive papers, buy from someone who will show you a lot-specific COA, and do not pay for ultra-pure material to run a pilot.

What SS-31 costs, and what you are paying for

People are often surprised that SS-31 is cheaper per milligram than many longer peptides. It should be. There are only three coupling steps in the synthesis, and the purification is quick because there are few by-products to separate.

The one costly ingredient is the dimethyltyrosine. It is a specialty amino acid, made in small volumes, and it accounts for a good part of the raw material bill. The rest of the price is labour, analysis, freeze-drying, vials and shipping.

Our own prices run from $39 for a 5 mg Standard Grade vial to $1,599 for a 500 mg Bulk Research Grade vial. Per milligram, that is under eight dollars at the small end and a little over three at the large end. The step up from Standard to Ultra-Pure adds roughly half again to the price of a given size. Whether that is worth it depends entirely on what the material is for, which is why we keep saying to decide that first.

A quick way to sanity-check any quote for SS-31: divide the price by the milligrams, then ask whether the weight is net peptide or gross powder. Two offers that look thirty percent apart can turn out to be the same once you correct for that.

Who actually orders it

It may help to know who else is buying. Our orders come from four kinds of customer.

University labs working on mitochondrial biology, ageing, kidney or heart models. They tend to order High Purity or Ultra-Pure in 10 mg and 25 mg vials, a box at a time, on a steady rhythm through the academic year.

Contract research organisations running studies for someone else. They want Ultra-Pure, full paperwork, one lot for the whole study and a quote on letterhead. They ask the most questions before ordering and the fewest afterwards.

Analytical labs that use SS-31 as a reference material for method development. They buy small quantities of the highest grade and care more about the certificate than the price.

Resellers and distributors who supply labs in their own country. They buy Bulk grade or large mixed orders and usually want a standing arrangement.

If you are in one of those groups, tell us which when you write. It lets us skip the generic reply and go straight to what you are likely to need.

A short glossary

A few terms come up in every conversation about this compound. If you are new to peptides, these are the ones worth knowing.

• Lyophilized. Freeze-dried. The form in which the powder ships.
• Reconstitute. To dissolve the powder in a liquid before use.
• COA. Certificate of Analysis, the document reporting test results for a specific lot.
• Lot or batch. One production run. Everything from the same lot was made and tested together.
• HPLC purity. The share of the peptide material that is the intended compound, as measured by liquid chromatography.
• Net peptide content. The share of the powder weight that is actually peptide, once salts and water are subtracted.
• Counter-ion. The negative ion paired with the positively charged peptide. Usually acetate or trifluoroacetate.
• Cardiolipin. The mitochondrial membrane lipid that SS-31 binds.
• In vitro. In glassware or culture, as opposed to in a living animal.

None of these is complicated once you have seen it used a couple of times. If a supplier uses a term you do not recognise and will not explain it, that is useful information about the supplier.

When SS-31 is the wrong choice

It is only fair to say when not to buy it. If your question is about general oxidative stress in the cell body and not about mitochondria, a cheaper untargeted antioxidant will tell you more. If your cells are healthy and you are hoping for a boost, SS-31 is unlikely to give you one. And if what you need is a medicine for a person, a research vial is not that. We would rather lose a sale than have someone order the wrong thing and feel misled afterwards.

Common questions about SS-31

Is SS-31 the same as elamipretide?

Yes. Elamipretide is the international non-proprietary name for the same molecule. MTP-131 and Bendavia are older labels for it. The Wikipedia entry for elamipretide lists them all.

What does SS-31 look like when it arrives?

A small amount of white to off-white powder or a thin cake at the bottom of a sealed glass vial. Five milligrams is not much to look at. That is normal. Do not judge the fill by eye.

Can I order fewer than 50 units?

Our standard terms are wholesale. If you need a smaller quantity to evaluate before committing, write to us and explain. We deal with that case by case.

How fast do you ship?

We confirm by email first, then ship once payment is received. Tell us in your enquiry if you are working to a deadline and we will tell you honestly whether we can meet it.

Do you provide a COA with SS-31?

Every order ships with the Certificate of Analysis for its lot. You can also ask to see it before you order.

That is the short version of what we know about SS-31. When you are ready, the sizes and current prices are on the SS-31 peptide page, and the contact form is the quickest way to reach us.