SS-31 (elamipretide) peptide: sequence, how it is supplied, COA, sizes

SS-31 is a synthetic peptide of four residues.

The initials stand for Szeto and Schiller, the two chemists who designed a series of short, positively charged, aromatic peptides in the early 2000s; the number is the position of this one in the series.

The same molecule was later coded MTP-131 and given the international name elamipretide. Three names, one sequence.

The design alternates basic and aromatic residues (basic-aromatic-basic-aromatic), which is what lets the short chain bind cardiolipin, a lipid found in the inner mitochondrial membrane, in the cell-free experiments described in the publications below.

The same sequence was licensed in 2025 under a trade name for one rare indication; what is sold as SS-31 for research is the identical tetrapeptide, made by solid-phase synthesis, purified by preparative HPLC and freeze-dried.

Research use only. Not for human or veterinary use.

Of the four residues, two are not among the twenty amino acids of proteins, and both change how the peptide is made and certified.

D-arginine at position 1 is the mirror image of the natural L-arginine. It is there so that the peptide is not cleaved by aminopeptidases, which recognize only L-residues.

On a certificate it is invisible to HPLC and mass spectrometry (an enantiomer has the same mass and, on an ordinary column, the same retention time); only a chiral analysis or the synthesis record confirms it.

A supplier that buys the D-Arg building block from a named vendor and states it on the certificate has answered the question; one that does not has left it open.

2′,6′-dimethyltyrosine (Dmt) at position 2 is a tyrosine with two methyl groups added to the aromatic ring.

It is a costly building block, roughly a hundred times the price of tyrosine per gram, and the single largest item in the cost of the peptide.

Its presence is confirmed by mass: the two methyls add 28.0 daltons, so a "SS-31" whose mass reconstructs to 611.8 instead of 639.8 was made with plain tyrosine and is a different molecule.

HPLC purity: one main peak

On reverse-phase HPLC the tetrapeptide elutes as a single sharp peak; the purity figure is the area of that peak against all peaks. Above 99 % is the specification for the catalog lots.

With only four residues, the deletion sequences that plague longer peptides are few; the impurities to look for are the des-methyl variant (tyrosine in place of Dmt, eluting slightly earlier) and the free acid (C-terminal OH instead of NH₂, +1 dalton, eluting later).

Mass spectrometry: 640.4 and 320.7

A 640-dalton peptide with three basic sites is seen by electrospray ionization as the singly charged ion at m/z 640.4 [M+H]⁺ and the doubly charged ion at 320.7 [M+2H]²⁺.

Both reconstruct to 639.8. A reconstructed 611.8 is the des-methyl peptide; 640.8 is the free acid.

Net peptide content, counter-ion, water

A peptide with three basic sites carries three counter-ions, and for a molecule this small they weigh a lot: as the triacetate, 639.8 g of peptide comes with 180.2 g of acetate, so the net peptide content of a pure lyophilized acetate salt cannot exceed 78 %, and 70 to 75 % after residual water is the realistic figure.

A certificate that reports 95 % net content for an SS-31 acetate salt has measured something else.

If the salt is the trifluoroacetate (from an HPLC purification that was not exchanged), the counter-ions weigh 342 g and the ceiling falls to 65 %; the certificate must state the salt.

What else must be on the page

• The laboratory's name and a verifiable test number (Janoshik Analytical is the reference in this market).
• The lot number, with the task number and verification key the laboratory confirms.
• The test date and a photograph of the tested vial wearing the supplier's label.

The OXpeptides Janoshik reports are published per size in the COA library and on the SS-31 product page.

The field-by-field method is in how to read a peptide COA, and the way to check a report number against the laboratory itself is in how to read a Janoshik test report.

SS-31 is stocked in one size, 10 mg: 10 mg of a 640-dalton peptide is 15.6 micromoles, a quantity that suits the bench, and the Dmt building block makes smaller fills uneconomical per milligram.

It is listed with the two other mitochondrial reagents the same laboratories order, MOTS‑c (the 16-residue mitochondrial-derived peptide) and NAD⁺.

The catalog card at the top of this page reads the live price; volume tiers apply from two vials, and the subscription price applies to every delivery.

What the price includes at OXpeptides: a sealed, labeled vial and analysis in progress, report published as soon as it is received. Ships from the EU · tracked: €9.90, free from €120.

See SS-31 in the catalog →

Two names return the same molecule in a bibliographic search, and knowing both saves a wasted afternoon: SS-31, the Szeto-Schiller series number, and elamipretide, the international non-proprietary name.

A third, MTP-131, appears in older records. All three point at D-Arg-Dmt-Lys-Phe-NH₂.

What the literature characterises is the interaction of that tetrapeptide with cardiolipin, the phospholipid of the inner mitochondrial membrane, and the consequences for membrane organisation in cell and tissue models.

The two papers listed at the end of this page are the ones every later article cites back to; a bibliography that cites neither is a bibliography assembled from other shop pages.

For a laboratory choosing between the two mitochondrial reagents in the catalog, the separation is chemical and not editorial.

SS-31 is a four-residue synthetic sequence with two non-proteinogenic residues, 639.8 g/mol. MOTS‑c is a sixteen-residue peptide encoded in the mitochondrial genome itself, 2,174.6 g/mol. They share a compartment and nothing else.

• Temperature: −20 °C for long-term storage; a refrigerator (2 to 8 °C) for a few weeks.
• Light: the dimethyltyrosine ring is a phenol, and phenols oxidize slowly in light and air; keep the vial in its box.
• Moisture: a salt with three counter-ions is hygroscopic. Keep it sealed; let a cold vial reach room temperature before it leaves its bag.
• Shelf life: 24 months for a sealed lyophilized vial stored cold; the date on the label governs. In solution the peptide is stable for days at 4 °C, which is unusual among short peptides and is due to the D-residue and the amide terminus.

A few days of ambient shipping do not degrade the sealed powder. The rules compound by compound are in lyophilized peptides: storage and shelf life.

"SS-31 peptide" returns journal articles, videos and forum threads before it returns a research supplier. For a laboratory that needs the reagent, the listing that matters answers five questions on the page itself.

1. Is the mass 639.8? A certificate reconstructing to 611.8 is the des-methyl peptide; the Dmt residue is the whole cost of the molecule and the first thing a cheap lot leaves out.
2. Is the salt stated, with a net content that is arithmetically possible (below 78 % for the acetate, below 65 % for the trifluoroacetate)?
3. Is the COA from a named independent laboratory, verifiable on the lab's site, showing the supplier's labeled vial, with a task number and verification key the laboratory confirms?
4. Does the vial ship from domestic stock, tracked, in a few days? The catalog ships from our EU stock, tracked, to the European Union, Switzerland and Norway.
5. Does the page describe the reagent only (sequence, purity documentation, storage), with "research use only" stated plainly?

The seven-point method is in how to check a peptide supplier; the Europe-wide checklist in where to buy research peptides in Europe.

Once the vial is on the bench, the mass-to-volume arithmetic is on the bacteriostatic water calculator.