MOTS-c and SS-31 Are Not Two Versions of the Same Idea. One Is a Signal, One Is a Scaffold.

They are not two versions of one compound.

I sell one of them. MOTS-C 40mg is on our site, purity stated at ≥99%, COA attached. I have no commercial interest in SS-31 or elamipretide at all, no listing, no supplier, no plans. Weight everything below accordingly. I keep coming back to this pair because the mistake people make when they compare them is not a preference mistake. It is a category mistake, and category mistakes cost more, because you end up misreading whatever you observe.

Ask "which mitochondrial peptide is better" and you have already lost. Both names live in the mitochondrion. That is the extent of the overlap.

Signal vs. Scaffold

Two questions, in this order.

One: does the compound carry a message out of the mitochondrion, or hold structure inside one?

Two: does its literature live in models of metabolic dysregulation, or models of mitochondrial damage?

MOTS-c answers signal, dysregulation. SS-31 answers scaffold, damage.

The cleanest documented example of MOTS-c behaving like a signal is not a hand-wave about metabolism. Biotinylated MOTS-c pull-down with mass spectrometry identified BACH1, a transcription repressor, as a direct binding partner. MOTS-c binds competitively at the D560 residue, displaces the deubiquitinase USP7, and pushes BACH1 into K33-linked polyubiquitination and proteasomal degradation. In human umbilical vein endothelial cells stressed with taurocholic acid, MOTS-c attenuated oxidative stress and apoptosis, and overexpressing BACH1 abolished that protection, which pins the effect to the BACH1/SLC25A51 axis. That is a message with a delivery address. It is also cells in a dish, so hold it loosely.

SS-31, elamipretide, is a tetrapeptide: D-Arg-Dmt-Lys-Phe-NH2. Its entire design premise is going in and staying in. The net +3 charge and the spatial arrangement of its cationic and aromatic side chains are described as required for selective interaction with cardiolipin at the inner mitochondrial membrane.

You can tell what the field believes by how it builds the analogues. RI-4FPhe-SS31 is a proposed retroinverso version with a 4-fluorophenylalanine substitution: the backbone flip to resist endogenous peptidases, the fluorine to block CYP450-mediated aromatic hydroxylation, two separate metabolic vulnerabilities of the parent. The prediction is a longer plasma half-life while preserving that +3 charge and that side-chain geometry.

Nobody protects geometry on a messenger. You protect geometry when the molecule has to fit something.