What is SS-31 chemically?

It is a tetrapeptide, four residues, with the sequence D-Arg-Dmt-Lys-Phe-NH2. Two features stand out. The first residue is D-arginine rather than the natural L form, and Dmt is 2,6-dimethyltyrosine, a modified aromatic residue. Those non-standard components make the chain resistant to the peptidases that would rapidly degrade an ordinary four-residue peptide. The C-terminus is an amide rather than a free acid, written NH2.

Why is SS-31 described as mitochondria-targeted?

Because it concentrates inside mitochondria without needing a receptor or a transporter to carry it there. The molecule carries a net positive charge, and the inner mitochondrial membrane maintains a strong electrochemical gradient with a negative interior. Positively charged molecules are therefore drawn across and accumulate, reaching concentrations in the membrane region far above those in the surrounding cytosol. The targeting is a consequence of physics rather than biology, which is what makes the design elegant.

What is cardiolipin and why does it matter here?

Cardiolipin is a distinctive phospholipid found almost exclusively in the inner mitochondrial membrane, where it is involved in organising the protein complexes of the electron transport chain. SS-31 is studied for its association with cardiolipin, and much of the published reasoning about the compound runs through that interaction: if cardiolipin organisation affects how efficiently those complexes work, a molecule that binds it is a tool for probing that relationship.

Is SS-31 the same as elamipretide?

They refer to the same molecule. SS-31 is the research designation from the Szeto-Schiller series, elamipretide is the international non-proprietary name assigned for pharmaceutical development, and MTP-131 is a development code that also appears in the literature. Encountering all three names for one compound is normal and is a common source of confusion when searching.

Is SS-31 an approved medicine?

No. It has been the subject of clinical investigation, which distinguishes it from compounds that have never left preclinical work, but it holds no marketing authorisation in the UK and is not a licensed medicine here. Material sold under this name is supplied for in-vitro laboratory research only.

No. We do not stock SS-31 and there is no Certificate of Analysis for it in our library. This guide exists because the compound draws steady search interest and the available information is mostly product copy.

What is SS-31?

7 min read · Updated October 2026 · MY PEPTIDES Research Team

Key facts

SS-31 is a synthetic tetrapeptide with the sequence D-Arg-Dmt-Lys-Phe-NH2, also referred to in the literature as elamipretide and as MTP-131. It belongs to a family of Szeto-Schiller peptides designed to concentrate inside mitochondria, and it is studied for its association with cardiolipin, a phospholipid found in the inner mitochondrial membrane. Its targeting does not depend on a receptor: the molecule carries a net positive charge and is drawn to the inner membrane by the electrochemical gradient across it, which is why it accumulates there at much higher concentrations than in the surrounding cytosol. Preclinical and in-vitro research examines it in the context of mitochondrial function and oxidative stress across a range of tissue models. It has been the subject of clinical investigation but holds no marketing authorisation in the UK. MY PEPTIDES does not stock SS-31. General information for laboratory context only, not medical advice.

The short answer

SS-31 is a four-residue peptide that goes where almost nothing else goes on purpose: inside the mitochondrion, specifically to the inner membrane. It does this without a receptor, a transporter or any biological machinery at all. It is positively charged, the inside of that membrane is strongly negative, and the molecule is simply pulled in and concentrated.

Once there it is studied for its association with cardiolipin, the phospholipid that helps organise the protein complexes of the electron transport chain. You will also find the same molecule called elamipretide or MTP-131 depending on which literature you are reading.

The targeting is the interesting part

Most attempts to direct a compound to a particular place in a cell involve attaching it to something that gets recognised and carried. That approach is fiddly, often inefficient, and adds bulk to the molecule.

SS-31 belongs to a family, the Szeto-Schiller peptides, that exploits something simpler. A working mitochondrion maintains a substantial electrochemical gradient across its inner membrane, with the matrix side negative relative to the outside. That gradient is how the organelle stores the energy it uses to make ATP, and it is a permanent feature of a functioning cell. A small molecule carrying net positive charge experiences that gradient as a force, crosses, and accumulates. Reported concentrations in the membrane region run far above those in the surrounding cytosol.

Two consequences follow for anyone using this as a research tool. The accumulation depends on the membrane potential, so it is not uniform across cells in different metabolic states, which can be an experimental variable rather than a constant. And the non-standard residues, the D-arginine and the dimethyltyrosine, are what let a four-residue chain survive long enough to get there at all. An ordinary tetrapeptide of natural L-amino acids would be cleaved well before it had the chance.

What the literature examines

The published in-vitro and preclinical work looks at SS-31 in the context of mitochondrial function and oxidative stress, across a reasonably wide range of tissue models. The reasoning in most of it runs through cardiolipin: the compound associates with that phospholipid, cardiolipin organisation is implicated in how efficiently the electron transport chain operates, and so the peptide becomes a way to interrogate that link.

This compound has also been through clinical investigation, which genuinely distinguishes it from most of what is discussed under the research-compound heading. That is a meaningful difference in evidence base, and it is also frequently overstated in marketing copy. Having been studied in humans is not the same as having been shown to work in humans, and it is certainly not the same as approval. Clinical programmes produce negative results as often as positive ones, and a compound can accumulate a substantial trial literature without ever reaching authorisation.

As always, the observations in any individual study belong to the model, the concentration, the exposure and the endpoint that study used.

What the research does not establish

SS-31 holds no marketing authorisation in the UK and is not a licensed medicine here. It therefore cannot lawfully be supplied for human medicinal use, regardless of how it is described, and the Human Medicines Regulations 2012 rather than the Misuse of Drugs Act are the provisions that matter. Our guide on whether peptides are legal in the UK sets out that framework.

The practical reading: material offered under this name is supplied for in-vitro laboratory research. Where a seller frames it as anything else, treat that as information about the seller.

A note on handling

Short peptides with modified residues are generally more robust than their length suggests, and that applies here. The usual constraints still hold: temperature, light and time all matter, freeze-thaw cycling is a stress worth avoiding, and the pH of whatever you dilute into is set by your buffer rather than by the diluent. Our guides on storing research peptides and bacteriostatic water and solution stability cover the general discipline.

One point specific to this compound: because its accumulation depends on an intact membrane potential, experimental conditions that alter mitochondrial state will alter how much of it ends up where you think it is. That is worth designing around rather than discovering afterwards.

Where MY PEPTIDES stands

We do not stock this compound. There is no Certificate of Analysis for it in our library and no product page for it on this site, and this guide is not an offer to supply it. If that ever changes it will change by a product appearing in the catalogue with a batch certificate attached, not by a line in a guide.

What we do supply, and the documentation standard we hold it to, is set out in our guide on certificates of analysis.

The bottom line

SS-31, also called elamipretide, is a mitochondria-targeted tetrapeptide whose unusual property is that it concentrates in the inner mitochondrial membrane by charge rather than by any biological transport. It is studied in relation to cardiolipin and mitochondrial function, has been through clinical investigation without reaching UK authorisation, and is not something we supply.

All compounds referenced on this site are discussed strictly in the context of in-vitro laboratory research. Nothing here is a medicine, a supplement or a therapeutic product, nothing here describes administration to humans or animals, and this guide is general information rather than medical, legal or research advice.

Frequently asked questions

What is SS-31 chemically?: It is a tetrapeptide, four residues, with the sequence D-Arg-Dmt-Lys-Phe-NH2. Two features stand out. The first residue is D-arginine rather than the natural L form, and Dmt is 2,6-dimethyltyrosine, a modified aromatic residue. Those non-standard components make the chain resistant to the peptidases that would rapidly degrade an ordinary four-residue peptide. The C-terminus is an amide rather than a free acid, written NH2.
Why is SS-31 described as mitochondria-targeted?: Because it concentrates inside mitochondria without needing a receptor or a transporter to carry it there. The molecule carries a net positive charge, and the inner mitochondrial membrane maintains a strong electrochemical gradient with a negative interior. Positively charged molecules are therefore drawn across and accumulate, reaching concentrations in the membrane region far above those in the surrounding cytosol. The targeting is a consequence of physics rather than biology, which is what makes the design elegant.
What is cardiolipin and why does it matter here?: Cardiolipin is a distinctive phospholipid found almost exclusively in the inner mitochondrial membrane, where it is involved in organising the protein complexes of the electron transport chain. SS-31 is studied for its association with cardiolipin, and much of the published reasoning about the compound runs through that interaction: if cardiolipin organisation affects how efficiently those complexes work, a molecule that binds it is a tool for probing that relationship.
Is SS-31 the same as elamipretide?: They refer to the same molecule. SS-31 is the research designation from the Szeto-Schiller series, elamipretide is the international non-proprietary name assigned for pharmaceutical development, and MTP-131 is a development code that also appears in the literature. Encountering all three names for one compound is normal and is a common source of confusion when searching.
Is SS-31 an approved medicine?: No. It has been the subject of clinical investigation, which distinguishes it from compounds that have never left preclinical work, but it holds no marketing authorisation in the UK and is not a licensed medicine here. Material sold under this name is supplied for in-vitro laboratory research only.
Do you sell SS-31?: No. We do not stock SS-31 and there is no Certificate of Analysis for it in our library. This guide exists because the compound draws steady search interest and the available information is mostly product copy.