Buying MOTS-c in the USA: What Mitochondria-Derived Means
Two compounds in this catalog are routinely called mitochondrial peptides, and the word is doing completely different work in each case. One is named for where its gene sits; the other for where the molecule was engineered to go. Mixing them up is easy, and it leads to expecting the wrong things from a certificate.
Derived from the mitochondrion, literally
MOTS-c stands for mitochondrial open reading frame of the twelve-S ribosomal RNA type-c — a statement about genetic origin, not about the molecule. Nearly every protein that does a job inside a mitochondrion is encoded in nuclear DNA and imported afterwards. MOTS-c is not. Its reading frame sits inside the mitochondrial genome itself, nested in the 12S rRNA gene, in a frame overlapping a sequence whose main role is structural rather than protein-coding.
That nesting is the whole reason the class drew attention. The mitochondrial genome is small and was assumed for a long time to encode a short, fixed list of products. A peptide whose reading frame hides inside one of its RNA genes is a different sort of discovery from another analog coming off a synthesizer.
Sequence and identity figures
Sixteen residues: Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg. Molecular formula C101H152N28O22S2, mass around 2174.6 g/mol, CAS registry number 1627580-64-6.
Two features of that formula carry the analytical consequences: the S2, which is two sulfur atoms, and an aromatic content that is high for a peptide this short.
Two methionines means two oxidation peaks
Both sulfurs sit in methionine thioethers, at positions 1 and 6, and a methionine thioether oxidizes to the sulfoxide easily — on contact with air, with light, or with a peroxide-contaminated solvent. Each oxidation event adds one oxygen: 16 daltons.
With two methionines the ladder has two rungs instead of one. A peak 16 Da above the expected mass is singly oxidized material; 32 Da above it is doubly oxidized. Both are different compounds from the one on the label, and neither is necessarily a synthesis fault, because oxidation can happen long after manufacture. A clean certificate describes the material as tested, not as it will remain. The discipline that follows is obvious: few vial entries, powder kept dry and dark. How peptides degrade covers the routes.
Detection is the easy part with this one
The sequence holds a tryptophan, two tyrosines and a phenylalanine — a lot of chromophore. MOTS-c therefore responds strongly at 280 nm as well as at the usual 214 nm, and a purity figure at either wavelength carries information.
That is not true across the board. A sequence with no aromatic residues, Selank for instance, is close to invisible at 280 nm, and a purity figure taken there says almost nothing. Knowing which case you are in before you read the number is the point; what a third-party peptide test actually measures works through it.
Three arginines, one lysine, and a tailing peak
MOTS-c is strongly basic — four positively charged residues on a backbone that also carries substantial hydrophobic content in isoleucine, leucine and phenylalanine. That mixed character shows up on a reversed-phase column, and basic peptides tail when they interact with residual silanols on older column chemistries.
A tailing peak inflates or deflates an integrated area depending on where the baseline is drawn, which is one of the mundane reasons two laboratories report different numbers for the same vial. Why two certificates can disagree covers the rest of them.
SS-31 is targeted, not derived
SS-31 is four residues, fully synthetic, and encoded nowhere at all. Its relationship to mitochondria is that the molecule was built around an alternating aromatic-cationic motif that associates with cardiolipin, a phospholipid largely restricted to the inner mitochondrial membrane. That is a delivery property, not a genetic one.
MOTS-c is mitochondrial by origin; SS-31 is mitochondrial by destination. Nothing about one predicts anything about the other. SS-31 and cardiolipin covers that mechanism, and mitochondrial peptides covers the literature on both.
What to look for on a certificate
Measured mass against the calculated 2174.6, with an eye on anything at 2190 or 2206 — the singly and doubly oxidized forms. The detection wavelength. The chromatogram itself rather than a summary figure, so that tailing and shoulders are visible. And net peptide content, which accounts for counter-ion and residual water and is what tells you how much peptide is in the vial; see net peptide content. Every report we hold is published in full on the certificates of analysis page.
Names you will see
MOTS-c, MOTS-C, MOTSc, and the sequence MRWQEMGYIFYPRKLR. All of them are the same sixteen-residue peptide.
What we supply
MOTS-c is stocked as a 10mg vial and a 20mg vial, lyophilized, with identity data published on each product page. Supplied for laboratory research use only. We publish no dosing information, no protocols involving human or veterinary subjects, and no statements about what the compound does in a person — and we do not provide them on request.