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.
Table of Contents
Table of Contents
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.