Peptide reference · 16-residue mitochondrial-derived peptide

MOTS-c COA check: molecular weight, formula and what to look for

By the PeptideCOACheck team · Last updated November 2, 2026 · How we check

Use these reference values to check the identity result on a MOTS-c Certificate of Analysis. The theoretical average molecular weight of MOTS-c is 2,174.59 Da and the monoisotopic mass is 2,173.108 Da.

Check a MOTS-c COA now

FP · 2,173.1077 Fingerprint calculated from the formula: positions of the protonated ions, the natural isotope pattern of the neutral molecule (relative heights are calculated; ion heights are schematic) and the atom mix. It is a reference picture, not measured data.

MOTS-c reference data

Name	MOTS-c
Also known as	Mitochondrial ORF of the 12S rRNA type-c
Type	16-residue mitochondrial-derived peptide
Molecular formula	C₁₀₁H₁₅₂N₂₈O₂₂S₂
Average molecular weight	2,174.59 g/mol (Da)
Monoisotopic mass	2,173.1077 Da
Residues	16
Sequence	Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg
Reference source	PubChem CID 146675088 (formula and mass cross-checked)

Expected mass spectrometry ions

A MOTS-c COA may list one of these m/z values instead of the neutral mass. That is still consistent with MOTS-c. How charge states work.

Ion	m/z (monoisotopic)	m/z (average)
[M+H]⁺	2,174.11	2,175.60
[M+2H]²⁺	1,087.56	1,088.30
[M+3H]³⁺	725.38	725.87
[M+4H]⁴⁺	544.28	544.65

What else can show up on a MOTS-c COA

Masses calculated from MOTS-c's formula and sequence for the adducts, degradation products and synthesis impurities a lab report can show. A match tells you what the extra peak probably is.

Signal	Value	What it means
Na adduct, deconvoluted (M + 21.98)	2,195.09 Da	Sodium adduct: an MS artifact, not a separate impurity. The [M+Na]+ ion itself is at M + 22.99
K adduct, deconvoluted (M + 37.96)	2,211.06 Da	Potassium adduct: an MS artifact. The [M+K]+ ion itself is at M + 38.96
TFA adduct (M + 113.99)	2,287.10 Da	Trifluoroacetic acid from purification seen as an adduct; residual TFA salt is real vial content
M + 16 (oxidation)	2,189.10 Da	Oxidation of Met/Trp
M + 32 (double oxidation)	2,205.10 Da	Two oxidations, or one Met to sulfone / one Trp to N-formylkynurenine
M + 0.98 (deamidation)	2,174.09 Da	Asn/Gln deamidation; overlaps the natural isotope peak, needs high-resolution MS

Deletion sequences (11): one residue missing

Signal	Value	What it means
des-Met (M − 131.04)	2,042.07 Da	Deletion sequence missing one Met
des-Arg (M − 156.10)	2,017.01 Da	Deletion sequence missing one Arg
des-Trp (M − 186.08)	1,987.03 Da	Deletion sequence missing one Trp
des-Gln (M − 128.06)	2,045.05 Da	Deletion sequence missing one Gln
des-Glu (M − 129.04)	2,044.07 Da	Deletion sequence missing one Glu
des-Gly (M − 57.02)	2,116.09 Da	Deletion sequence missing one Gly
des-Tyr (M − 163.06)	2,010.04 Da	Deletion sequence missing one Tyr
des-Leu/Ile (M − 113.08)	2,060.02 Da	Deletion sequence missing one Leu/Ile
des-Phe (M − 147.07)	2,026.04 Da	Deletion sequence missing one Phe
des-Pro (M − 97.05)	2,076.05 Da	Deletion sequence missing one Pro
des-Lys (M − 128.09)	2,045.01 Da	Deletion sequence missing one Lys

Adduct rows are deconvoluted masses (the shift seen against [M+H]⁺); the singly charged [M+Na]⁺ ion itself sits at M + 22.99. Deletion masses alone can't say which copy of a repeated residue is missing.

For MOTS-c, 98% or higher HPLC purity is the usual research-grade benchmark. The full checklist is in how to read a peptide COA.

MOTS-c-specific things to watch

MOTS-c is a 16-residue peptide (about 2174.6 Da) encoded in mitochondrial DNA.

It contains two methionines and a tryptophan, all of which can oxidize. Extra peaks at +16 or +32 Da indicate oxidation, which becomes more likely as material ages, so test date matters.

Expect charge states such as [M+2H]²⁺ near 1087.6 m/z and [M+3H]³⁺ near 725.4 m/z.

MOTS-c has three arginines and a lysine, so ESI spectra are dominated by multiply charged ions: [M+2H]2+ near 1087.6, [M+3H]3+ near 725.4 and [M+4H]4+ near 544.3 m/z. A single [M+H]+ at 2174.1 is often weak or absent, and that is normal.

Its two methionines and one tryptophan make oxidation the main degradation risk: +16 Da (2189.1) and +32 Da (2205.1, either two oxidations or one methionine oxidized all the way to sulfone). A one-residue methionine deletion (2042.1 Da) points to a synthesis problem.

Regulatory note, as of November 2, 2026. On October 28, 2026, HHS issued an interim enforcement discretion policy for 503A pharmacy compounding of six peptides: BPC-157, Epitalon, KPV, MOTS-c, Semax and TB-500. It covers single-ingredient preparations made by state-licensed pharmacies and physicians under listed conditions; blends are not covered, and it does not approve these peptides as drugs. For reading a COA, the useful detail is that the policy names specific forms (here, MOTS-c acetate), so a COA that states the salt form tells you more than one that does not.

Compounds with similar mass

If a COA's mass is off, compare it with these neighbors. A match to one of them can point to a mislabeled product.

AOD-9604: 1,815.08 Da (-359.51 Da)
BPC-157: 1,419.54 Da (-755.05 Da)
Kisspeptin-10: 1,302.44 Da (-872.15 Da)

Sources

PubChem CID 146675088: MOTS-c formula and reference mass.
CIAAW: Standard atomic weights: Used to calculate average molecular weights.
NIST CODATA: proton mass: Used to convert m/z charge states to neutral mass.
PeptideCOACheck methodology: How the checker's thresholds work.
HHS will permit compounding of six peptides ahead of formal rulemaking (RAPS, Oct 29, 2026): Summary of the October 28, 2026 HHS enforcement discretion policy.
Federal Register public inspection, FR Doc 2026-22192: The policy document itself.

Last updated November 2, 2026. Written and maintained under our editorial policy. Found an error? See corrections.

Frequently asked questions

The COA lists 1087 and 725, not 2174. Is that right for MOTS-c?

Yes. Those are the 2+ and 3+ ions of the same 2173.1 Da molecule.

What does a MOTS-c peak 16 Da high mean?

One oxidized methionine or tryptophan. A large one suggests aged or poorly stored material.

What purity is believable for MOTS-c?

98% or higher for a 16-residue peptide. Check that the test date is recent, since oxidation grows with age.

For laboratory research use only. This page describes analytical chemistry data. It is not medical advice and makes no claim about effects in humans or animals.