SS-31 is four residues long and two of them are not standard amino acids. The sequence is D-Arg-Dmt-Lys-Phe-NH2: a D-arginine, a 2',6'-dimethyltyrosine, a lysine and a phenylalanine, with the C-terminus amidated. It belongs to the family of Szeto-Schiller peptides described by Zhao and colleagues in 2004, which were designed to accumulate in mitochondria, and it is sold here as a 10 mg lyophilized vial with a certificate for the lot. Its generic name is elamipretide.
This post reads the certificate, explains what the two unusual residues do to the chemistry and the handling, and states the regulatory fact that most research-peptide listings for this compound leave out.
What is unusual about the four residues?
| Residue | Position | What it is | What it does to the molecule |
|---|---|---|---|
| D-Arg | 1 | Arginine in the D-configuration | A positive charge, and a bond that proteases do not cut |
| Dmt | 2 | 2',6'-dimethyltyrosine, a tyrosine with two methyl groups on the ring | An aromatic phenol, more hydrophobic than tyrosine, oxidisable at the phenol |
| Lys | 3 | Lysine | A second positive charge |
| Phe-NH2 | 4 | Phenylalanine with an amidated C-terminus | An aromatic ring, and no C-terminal negative charge |
The design is alternating: basic, aromatic, basic, aromatic. With the N-terminal amine, the molecule carries three positive charges at neutral pH and no negative ones. That pattern is what the 2004 paper identified as giving cell permeability and mitochondrial accumulation, and Birk and colleagues in 2013 reported that the peptide interacts with cardiolipin, the mitochondrial inner-membrane lipid. Formula C32H49N9O5, mass 639.8.
The mass is worth checking by hand because of the non-standard residues. Arginine 174.20, dimethyltyrosine 209.25, lysine 146.19 and phenylalanine 165.19 sum to 694.83; three peptide bonds remove 54.05, giving 640.78; converting the C-terminal acid to an amide replaces OH with NH2, which is minus 0.98, giving 639.80. The certificate reports 639.8.
What does lot SS31-10-0803 report?
COA7584, issued by Bioviridian Inc. on 17 August 2026. Five tests.
| Test | Method | Result | What it establishes |
|---|---|---|---|
| Identity | LC-MS/MS | 639.8 observed | The predicted mass for D-Arg-Dmt-Lys-Phe-NH2, with a fragment pattern that fits |
| Purity | RP-HPLC, 214 nm | 99.77% | 99.77% of the UV-absorbing area is the main peak, retention 6.19 minutes |
| Content | Gravimetric against label | 10.44 mg | Four percent over the 10 mg label |
| Endotoxin | LAL | < 0.05 EU/mL | Below the reporting limit |
| Heavy metals | ICP | < 0.01 ppm | Below the reporting limit |
Two aromatic residues give this small peptide more retention than its size suggests, 6.19 minutes, which is enough to separate it from the obvious impurities. The area-percent post covers why that matters. Note that mass spectrometry cannot by itself distinguish the D-arginine from an L-arginine, since enantiomers have the same mass; a chiral analysis would. The sequence verification post covers the limits of each method.
How many micromoles is 10 mg?
The label's 10 mg at 639.8 g/mol is 15.6 micromoles; the measured 10.44 mg is 16.3. For a compound used in the cell literature at nanomolar to low micromolar concentrations, one vial is a programme. The concentration table and the molarity post have the arithmetic. At the listed price of $70 the vial is about $4.50 per micromole.
How is it handled?
- Adsorption. Three positive charges and two aromatic rings: this is a peptide that sticks to plastic and glass. Low-binding tubes and tips at every dilution below micromolar; do not store dilute working solutions. The adsorption post has the mechanism.
- Oxidation. The dimethyltyrosine phenol can oxidise, more slowly than a methionine but faster than a plain tyrosine's. Keep solutions cold, and degas the diluent for sensitive assays.
- Light. No tryptophan, so light sensitivity is modest; amber tubes are still cheap.
- Solubility. High in water; the molecule is small and cationic.
- pH. Unbuffered solutions will be slightly basic; buffer the working stock as the pH and buffer post recommends.
- Storage. Lyophilized at minus 20 °C; solutions aliquoted and frozen.
- Diluent. Water or buffer. Reconstitution solution only for a preserved multi-entry stock, per the diluent post.
What is its regulatory status?
On 19 September 2025 the FDA granted accelerated approval to elamipretide hydrochloride, under the brand name Forzinity, for Barth syndrome, a rare inherited mitochondrial disease. Accelerated approval is conditional: continued approval depends on a confirmatory trial. The sponsor's announcement and trade reporting from that week are cited above.
That makes SS-31 an approved prescription drug in the United States, in a different formulation and through a different channel. It does not change what is in the vial sold here, which is the research-grade peptide with the certificate above, for laboratory research use only and not for human or animal use. It does change what an honest product page must say, and this site says it, as it does for melanotan-1. The research-use post and the legality post cover the frame.
Frequently asked questions
Is SS-31 the same molecule as elamipretide?
Yes. Elamipretide is the generic name for D-Arg-Dmt-Lys-Phe-NH2. The approved product is its hydrochloride salt in a pharmaceutical formulation.
Why does the certificate's purity method not see the D-configuration?
Because reversed-phase HPLC and mass spectrometry both respond to composition and mass, which enantiomers share. Distinguishing D-arginine from L-arginine needs a chiral method. The certificate reports what its methods measure.
What does the mass check prove?
That the lot contains the intact tetrapeptide at 639.8, which rules out deletion products, the free acid in place of the amide, and oxidised material. The LC-MS post explains the tolerance.
Why is it so prone to adsorption?
Three positive charges and two aromatic rings on a molecule of 640 daltons. Small cationic aromatic peptides are the worst case for surface loss, and dilute solutions should be made fresh.
Is the vial a medicine?
No. It is the research reagent, for laboratory use only. The same peptide is an FDA-approved medicine in a different formulation, and the product page says so.
References
- Zhao K, Zhao GM, Wu D, et al. Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury. Journal of Biological Chemistry 2004;279(33):34682-34690. doi.org/10.1074/jbc.M402999200
- Birk AV, Liu S, Soong Y, et al. The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. Journal of the American Society of Nephrology 2013;24(8):1250-1261. doi.org/10.1681/ASN.2012121216
- PubChem, National Library of Medicine. Elamipretide, CID 11764719, C32H49N9O5, CAS 736992-21-5. Read 2 October 2026. pubchem.ncbi.nlm.nih.gov/compound/11764719
- Stealth BioTherapeutics. Press release: FDA accelerated approval of Forzinity (elamipretide HCl) for Barth syndrome, 19 September 2025. www.prnewswire.com/news-releases/stealth-biotherapeutics-announces-fda-accelerated-approval-of-forzinity-elamipretide-hcl-the-first-therapy-for-progressive-and-life-limiting-ultra-rare-genetic-disease-barth-syndrome-302562058.html
- Bioviridian Inc. Certificate of analysis COA7584, lot SS31-10-0803, issued 17 August 2026. Verification code on the certificate. bioviridians.com/coa-search.html
Every product mentioned is sold for laboratory research use only and is not for human or animal use. Nothing on this page describes or recommends use of the material sold here in humans or animals.
