What Is MOTS-C? Sequence, CAS, and What Its COA Should Say

MOTS-C is one of the more interesting compounds to document, because almost everything that makes it distinctive on a certificate has nothing to do with what it is thought to do. It is a sixteen-residue peptide whose amino acid composition creates a specific, predictable analytical problem, and a certificate that does not address that problem is telling you less than it appears to.

This is a documentation guide, not a research guide. It covers what the molecule is, what its paperwork should say, and which impurities its own chemistry makes likely. It does not cover what MOTS-C does, and that is deliberate. A supplier is the wrong source for that question, and a supplier who volunteers an answer to it is showing you something about themselves rather than about the compound.

What MOTS-C is, chemically

MOTS-C is a peptide of sixteen amino acids, sequence Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg, or MRWQEMGYIFYPRKLR in the one-letter system. Both notations are set by international nomenclature rules rather than by convention, and both are written from the N-terminus to the C-terminus.^[3]

The name is an acronym rather than a brand. It stands for mitochondrial open reading frame of the 12S rRNA type-c, which describes where the sequence is encoded: not in the cell nucleus like most peptides you will encounter, but within the mitochondrial genome. UniProt lists it under accession A0A0C5B5G6, entry name MOTSC_HUMAN, with the recommended name “Mitochondrial-derived peptide MOTS-c” and the alternative name spelled out in full.^[1] That entry is Swiss-Prot reviewed, meaning it has been manually curated rather than automatically generated, which is the standard worth insisting on when you are checking a sequence.

The chemistry, from the public registry entry:^[2]

• CAS Registry Number: 1627580-64-6
• Molecular formula: C₁₀₁H₁₅₂N₂₈O₂₂S₂
• Molecular weight: 2174.6 g/mol for the free peptide
• Termini: free N-terminus and a free acid C-terminus, written H-MRWQEMGYIFYPRKLR-OH
• Length: 16 residues

UniProt lists the mass as 2175 and the chemical registry lists 2174.6. That is rounding, not disagreement. If a certificate quotes something materially different, that is worth a question, and the most common innocent explanation is that the figure describes a salt form rather than the free peptide. More on that below.

The thing that makes MOTS-C different on paper

Look again at the sequence and count the residues that are chemically fragile: Met at position 1, Trp at position 3, and Met again at position 6. Three of the sixteen residues, nearly one in five, are the specific amino acids that analytical chemists watch for oxidation.

Methionine oxidises readily to the sulfoxide. That reaction adds a single oxygen atom, which is roughly 16 daltons. MOTS-C has two methionines, so there are two obvious oxidised species, and their masses are simple arithmetic from the parent mass:

• 2174.6, the intact peptide
• ~2190.6, one methionine oxidised
• ~2206.6, both methionines oxidised

Tryptophan, at position 3, is the most light-sensitive of the standard amino acids and has its own oxidation chemistry. Between the two methionines and the tryptophan, MOTS-C is simply more exposed to oxidative degradation than a peptide of similar length built from more robust residues.

This is not a warning about the compound. It is a statement about what its own composition predicts, and it gives you something concrete to look for.

What that means for the certificate you should be asking for

Because the likely impurities are predictable, the certificate can be checked against them rather than simply read.

On the mass spectrometry result, the observed mass should match 2174.6 within the method’s tolerance. If the trace is shown rather than just summarised, the species at roughly +16 and +32 are the ones worth looking at, because those are the oxidation products the sequence predicts. A certificate that reports only a single number tells you the main peak was right; a certificate that shows the trace lets you see what else was in the vial.

On the purity result, remember what the number actually measures. Purity by HPLC is the area of the target peak relative to the total area of all peaks, so an oxidised species that separates cleanly shows up as an impurity and pulls the number down, which is the system working as intended. Our guide on what peptide purity is covers how that figure is produced and what the compendial method requires of the run before the result counts.^[5]

On the lot number, purity is measured per lot, not per product. A certificate for a different lot than the one in your hand is not evidence about your material. How to read a COA walks through each section line by line.

Purity versus what is actually in the vial

MOTS-C carries three arginines and one lysine, which makes it strongly basic, and peptides like it are routinely purified and supplied as a salt. The public registry entry lists a trifluoroacetate salt form explicitly alongside the free peptide.^[2]

This matters for a practical reason that has nothing to do with quality. Purity and net peptide content are different measurements. Purity describes how much of the peptide portion is the intended compound. Net peptide content describes how much of the vial’s total mass is peptide at all, as opposed to counterion, residual water and salts. A vial can be 99% pure and still be meaningfully less than 99% peptide by mass. The two figures are produced by different methods, net peptide content usually by amino acid analysis rather than by chromatography, which is why they can differ widely on the same material.

Neither number is the “real” one. They answer different questions, and a thorough certificate reports both.

Storage, and why it matters more here

General storage guidance applies to MOTS-C as it does to any lyophilized peptide: cold, dry, sealed, dark, and let a vial reach room temperature before opening it so that condensation does not introduce moisture. Our guide on shelf life and stability covers the reasoning, and how to store research peptides covers the practice.

The reason it deserves a little more attention with this particular sequence is the tryptophan. Light exposure is a real variable for Trp-containing peptides, so “dark” is doing more work here than it does for a sequence without one.

It is also worth knowing that the storage words on a label have defined meanings rather than casual ones. The compendial definitions are freezer, −25°C to −10°C; refrigerator, 2°C to 8°C; cold, any temperature not exceeding 8°C; and controlled room temperature, 20°C to 25°C.^[4] A supplier who says “store cold” without saying which of those they mean has not actually told you anything.

A checklist for a MOTS-C certificate

• The lot number matches the vial in your hand, not a representative sample.
• Identity confirmed by mass spectrometry, with an observed mass consistent with 2174.6 for the free peptide, or a stated and explained salt mass.
• Purity by HPLC, ideally with the chromatogram shown rather than only the percentage.
• Net peptide content reported separately, or the salt form stated so you know why it is not reported.
• Endotoxin, if the work is sensitive to it. Our endotoxin testing guide explains what the units mean and what they do not.
• The testing laboratory named, and independent of the seller.

Where this guide stops

Everything above is about identity, measurement and handling, because those are the questions a supplier can legitimately answer and can be held to. Questions about what MOTS-C does in any biological system are not ones we will answer, in either direction. That is what the published literature and your own experimental design are for, and a vendor page is the worst available substitute for both.

What we will do is make the paperwork verifiable. Every lot we publish is listed in our public COA register, with the purity figure, the test date, the testing laboratory and the downloadable certificates, including our lowest result. You can check any lot number before you buy rather than after. If you would rather test it yourself, our Don’t Trust Us, Test Us program replaces any vial you send to an independent laboratory, pass or fail.

Unfamiliar terms in this article are defined in the research peptide glossary, and the rest of our documentation guides are collected on the guides page.

For a step-by-step walkthrough of what a MOTS-C certificate should show, and how the two methionines and the tryptophan in the sequence drive the impurities you will see on it, read our MOTS-C documentation guide.

References

Sources are limited to curated sequence and chemical registries, compendial standards and nomenclature rules. Nothing here is cited for biological activity, and no supplier catalogue is used as a source. Each was checked on 14 August 2026.

1. UniProt Knowledgebase, entry A0A0C5B5G6 (MOTSC_HUMAN), Swiss-Prot reviewed. Recommended name “Mitochondrial-derived peptide MOTS-c”, alternative name “Mitochondrial open reading frame of the 12S rRNA-c”; sequence MRWQEMGYIFYPRKLR, length 16, listed mass 2175. UniProt entry.
2. PubChem Compound Summary, CID 146675088. CAS 1627580-64-6; C₁₀₁H₁₅₂N₂₈O₂₂S₂; molecular weight 2174.6; sequence H-MRWQEMGYIFYPRKLR-OH; trifluoroacetate salt listed among synonyms. Published by the National Center for Biotechnology Information. PubChem record.
3. IUPAC and IUBMB Joint Commission on Biochemical Nomenclature, Nomenclature and Symbolism for Amino Acids and Peptides (Recommendations 1983), published 1984, which sets the one-letter and three-letter symbol systems and the conventions for peptide notation. Full recommendations.
4. United States Pharmacopeia, General Chapter <659> Packaging and Storage Requirements, storage temperature definitions. Excerpted USP-NF standards, published by USP (PDF).
5. United States Pharmacopeia, General Chapter <621> Chromatography, PDG Stage 4, official 1 December 2022, which sets the system suitability an HPLC purity run must meet before its result counts. PDG harmonisation record.

Every lot at USA Made Peps is independently third-party tested. You can look up any lot’s COA, see the MOTs-C product page, or browse the catalog.

Still have questions? Our frequently asked questions page covers ordering, testing, storage and shipping.

Related reading: what >98% purity actually means.

All products are sold strictly for research use only (RUO) and are not for human or animal consumption.