SS-31: Research Reference

SS-31 is a synthetic four-residue peptide, D-Arg-Dmt-Lys-Phe-NH2, in which Dmt is 2′,6′-dimethyltyrosine, a tyrosine carrying two extra methyl groups on its ring. It is the lead compound of the Szeto-Schiller peptides, designed to concentrate at the inner mitochondrial membrane, and in clinical research the same molecule is called elamipretide.

This reference collects what a laboratory needs to know about SS-31 as a material: how its four residues behave in the vial, what it dissolves in, how it is handled at the bench and what to do when an order arrives. Each section below has its own page.

Molecular reference

Name	SS-31 (Szeto-Schiller peptide 31)
Also known as	Elamipretide, MTP-131, SS31
Sequence	D-Arg-Dmt-Lys-Phe-NH2 (Dmt = 2′,6′-dimethyl-L-tyrosine; C-terminal amide)
Residues	4
Molecular formula	C32H49N9O5
Molecular weight	639.8 g/mol
CAS number	736992-21-5

Formula, molecular weight, CAS number, synonyms and the sequence are from PubChem (CID 11764719).

Three features of that sequence explain most of its behaviour. The first residue is D-arginine, the mirror-image form of the natural amino acid, and the chain ends in an amide rather than a free acid; its developer credits these two changes with greatly enhanced stability against peptidase enzymes and describes SS-31 as water-soluble and very stable in solution (Szeto, British Journal of Pharmacology, 2014). It has no methionine, cysteine, asparagine, glutamine or aspartic acid, so the usual oxidation, deamidation and aspartate routes are absent. And its one reactive site is the Dmt phenol: dimethyltyrosine is what gives the peptide its ability to scavenge oxidants, and analogues without it lost that activity (Zhao et al., Journal of Biological Chemistry, 2004). A residue that reacts with oxidants in a cell can react with them in a vial too, which is why light and air are the things to manage.

What it is studied for

The Szeto-Schiller peptides were built on an alternating pattern of aromatic and basic residues. In cell and isolated-mitochondria work they crossed cell membranes, concentrated about 1000-fold at the inner mitochondrial membrane, reduced reactive oxygen species and limited mitochondrial swelling (Zhao et al., Journal of Biological Chemistry, 2004). Later work showed that SS-31 binds cardiolipin, a phospholipid found only in the inner mitochondrial membrane, and that this complex protected cristae structure in an animal kidney ischemia model (Birk et al., Journal of the American Society of Nephrology, 2013). Biophysical studies describe it as a polybasic peptide that settles into the membrane surface and changes its electrostatics without destabilising the bilayer (Mitchell et al., Journal of Biological Chemistry, 2020).

Under the name elamipretide it has been through human trials. In the 168-week open-label extension of the TAZPOWER trial in Barth syndrome, eight of ten participants reached the final visit and six-minute walk distance improved by a cumulative 96.1 metres from the extension baseline (Thompson et al., Genetics in Medicine, 2024). The phase 3 MMPOWER-3 trial in 218 adults with primary mitochondrial myopathy did not meet its primary endpoints on walking distance or fatigue (Karaa et al., Neurology, 2023). Its developer’s review reports an elimination half-life of about 4 hours in humans, similar to animal species (Szeto, 2014). A 2025 review summarises the wider trial programme (Tung et al., International Journal of Molecular Sciences, 2025).

Our summaries are in what is SS-31, SS-31 elamipretide trials and MOTS-c vs SS-31.

Stability

With only four residues and none of the usual weak points, SS-31 is chemically forgiving. Its slow route in solution is oxidation of the Dmt ring, which light, warmth and trace metals speed up. The SS-31 stability page covers that route, enzyme resistance, freeze-thaw and what visible changes mean.

Solubility

SS-31 carries three positive charges at the pH of bacteriostatic water and is highly water-soluble, so it dissolves readily without any acid. The SS-31 solubility guide explains why, which concentrations dissolve cleanly and what causes haze.

Handling

Bench practice for SS-31 is mostly about keeping the solution cold, dark, sterile and labelled. The SS-31 handling page lists the steps and the common mistakes.

On arrival

What a sealed vial should look like, why it travels without an ice pack and where it goes first are on the SS-31 on-arrival page.

Storage and reconstitution

Fridge and freezer windows, before and after mixing, are on how long SS-31 lasts. Water volumes and the concentration table for a 10 mg vial are on how much bacteriostatic water for an SS-31 10 mg vial.

FAQ

Short answers to the questions researchers ask most about storing, mixing and handling SS-31 are on the SS-31 FAQ.

Where to get it

Vistara Labs supplies SS-31 10 mg as a lyophilised vial for laboratory research, shipped within Canada by Canada Post Xpresspost. Certificates are on our lab reports page, and they state the identity confirmed for each batch. For a related mitochondrial research compound, see the MOTS-c research reference.