What mass should a MOTS-c COA show?

PubChem lists MOTS-c as C101H152N28O22S2 with an average mass of 2174.6 g/mol and a monoisotopic mass of 2173.11 Da. A certificate should show the expected and measured values and which kind of mass it used. A measured mass about 16 or 32 units higher suggests oxidation, and other differences can mean a different sequence altogether.

How do I know if my MOTS-c is real?

Send a sample from your vial for identity by mass spectrometry, which should find 2174.6 g/mol for the human sequence. Add HPLC for purity, which also shows oxidised forms, and an amount test with counter-ion content. A seller's certificate is only useful if it names your batch and the laboratory, gives a measured mass, and can be verified with the issuer.

Why does MOTS-c oxidise so easily?

Because it contains two methionines, at positions 1 and 6, and a tryptophan at position 3. Methionine is the amino acid most prone to oxidation and tryptophan follows it. Each added oxygen raises the mass by 16 units. A validated doping-control assay for MOTS-c includes two oxidation products, and a good purity report should name oxidised forms rather than fold them into one figure.

Can an ELISA confirm my MOTS-c?

Not as an identity test. A published comparison found that MOTS-c levels measured by a commercial ELISA could not be confirmed by LC-MS, and the two methods gave considerably different results. An antibody test shows that something reacted with the antibody. Mass spectrometry shows the molecule has the right mass, which is what identity testing needs.

Why might my MOTS-c test show less than the label?

Counter-ions are a likely reason. MOTS-c has five positively charged sites that can each carry a counter-ion such as trifluoroacetate, which adds weight without adding peptide. The vial could also be underfilled, or part of the peptide could be oxidised. A report that separates peptide content, counter-ion content and oxidised forms lets you tell these apart.

One of the 30 compound testing profiles

MOTS-c

MOTS-c is a 16-amino-acid peptide, MRWQEMGYIFYPRKLR (C101H152N28O22S2, average mass 2174.6 g/mol); a test should confirm that mass, look for oxidation at its two methionines and its tryptophan, and report the peptide content separately from its counter-ions.

MOTS-c is a 16-amino-acid peptide encoded by a short open reading frame within the mitochondrial 12S rRNA gene (Lee et al., Cell Metabolism, 2015), and the US FDA states it has identified no human exposure data on drug products containing it (FDA, bulk substances with safety risks).

Test your MOTS-c

Identity card

Formula: C101H152N28O22S2
Average mass: 2,174.6 g/mol
Monoisotopic mass: 2,173.11 Da
Length: 16 residues
Modifications: None: free N-terminal amine and free C-terminal acid (H-MRWQEMGYIFYPRKLR-OH)
Also sold as: MOTSc, Mitochondrial open reading frame of the 12S rRNA-c
Sequence: MRWQEMGYIFYPRKLR
Note: PubChem gives an average mass of 2174.6 g/mol and a monoisotopic mass of 2173.1077409 Da, recorded as 2173.11. The two sulfur atoms in the formula are Met1 and Met6. Among PubChem's synonyms for the record is "MOTS-c (human) (trifluoroacetate salt)"; the salt's weight is not part of this formula.

Source: PubChem CID 146675088, MOTS-c, Lee C et al. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis. Cell Metab. 2015;21(3):443-54.

Check a certificate's mass against these values with the mass checker, prefilled for MOTS-c.

What usually goes wrong with MOTS-c. Documented failure modes, with sources.

Two methionines and a tryptophan

MOTS-c starts with methionine, has a second at position 6, and a tryptophan at position 3 (PubChem). Methionine is the residue most susceptible to oxidation, with tryptophan next; methionine sulfoxide adds 16 Da and the sulfone 32 Da (Butré et al., Molecules, 2023). A validated doping-control assay for MOTS-c includes two oxidation products alongside the intact peptide (Knoop et al., Rapid Communications in Mass Spectrometry, 2019). With two methionines, a sample can carry singly and doubly oxidised forms at +16 and +32 Da, and oxidation can progress between filling and testing, so read the result with the vial's storage history.

Species variants of the sequence

MOTS-c is encoded in mitochondrial DNA, and the same doping-control assay included animal MOTS-c analogues as well as the human peptide (Knoop et al., 2019). Those variants have different sequences and so different masses. A vial labelled MOTS-c should contain the human sequence, MRWQEMGYIFYPRKLR; an accurate intact mass shows whether it does, and a peptide map shows where an unexpected sequence differs.

A heavy counter-ion load

MOTS-c carries arginine at positions 2, 13 and 16, lysine at 14 and a free N-terminal amine, five sites that can pair with a counter-ion. In synthetic peptides, the number of trifluoroacetate counter-ions follows the number of positive charges, and in one study trifluoroacetate reached up to 35% of the total weight of the peptide salts tested (Erckes et al., Pharmaceuticals, 2025). PubChem's synonym list for MOTS-c includes its trifluoroacetate salt. A vial filled by salt weight can therefore hold noticeably less peptide than its label with no other defect, which is why counter-ion content belongs on the same report as the amount.

Immunoassay numbers are not identity

When the doping-control group compared its LC-MS method with a commercial ELISA, the endogenous MOTS-c levels the ELISA reported could not be confirmed by LC-MS, and the two methods gave considerably different results (Knoop et al., 2019). An antibody-based result says something reacted with the antibody, not that the molecule has the right mass and sequence. The US FDA has also said MOTS-c may have complexities with regard to peptide-related impurities and characterisation of the active ingredient (FDA, bulk substances with safety risks).

Which tests matter most

LC-MSConfirms 2174.6 g/mol for the human sequence and shows singly and doubly oxidised forms at +16 and +32 Da.
HRMSAccurate mass separates the human peptide from animal variants and pins down which modification an unexpected peak carries.
HPLC-UVGives purity and separates oxidised forms and synthesis by-products from the intact peptide.
Counter-ion contentFive basic sites mean counter-ions can be a large share of the weight; this test lets the amount be stated as peptide.

Reading MOTS-c results

A measured mass that is off by an amount that does not fit oxidation (+16 or +32) suggests a different sequence, such as an animal variant or a synthesis error, and is worth a peptide map. The mass checker computes average and monoisotopic masses from a sequence, and the net peptide content lesson explains peptide content versus purity.

Public Tested.ph results

No public MOTS-c records yet

Each public MOTS-c record will appear here with its identity, HPLC purity and measured amount against the label, once the first vial is tested.

FIG 13Amount against the label

Questions about testing MOTS-c

What mass should a MOTS-c COA show?: PubChem lists MOTS-c as C101H152N28O22S2 with an average mass of 2174.6 g/mol and a monoisotopic mass of 2173.11 Da. A certificate should show the expected and measured values and which kind of mass it used. A measured mass about 16 or 32 units higher suggests oxidation, and other differences can mean a different sequence altogether.
How do I know if my MOTS-c is real?: Send a sample from your vial for identity by mass spectrometry, which should find 2174.6 g/mol for the human sequence. Add HPLC for purity, which also shows oxidised forms, and an amount test with counter-ion content. A seller's certificate is only useful if it names your batch and the laboratory, gives a measured mass, and can be verified with the issuer.
Why does MOTS-c oxidise so easily?: Because it contains two methionines, at positions 1 and 6, and a tryptophan at position 3. Methionine is the amino acid most prone to oxidation and tryptophan follows it. Each added oxygen raises the mass by 16 units. A validated doping-control assay for MOTS-c includes two oxidation products, and a good purity report should name oxidised forms rather than fold them into one figure.
Can an ELISA confirm my MOTS-c?: Not as an identity test. A published comparison found that MOTS-c levels measured by a commercial ELISA could not be confirmed by LC-MS, and the two methods gave considerably different results. An antibody test shows that something reacted with the antibody. Mass spectrometry shows the molecule has the right mass, which is what identity testing needs.
Why might my MOTS-c test show less than the label?: Counter-ions are a likely reason. MOTS-c has five positively charged sites that can each carry a counter-ion such as trifluoroacetate, which adds weight without adding peptide. The vial could also be underfilled, or part of the peptide could be oxidised. A report that separates peptide content, counter-ion content and oxidised forms lets you tell these apart.

Sources

Lee C et al. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell Metab. 2015;21(3):443-54, Cell Metabolism (PMC)
Knoop A, Thomas A, Thevis M. Development of a mass spectrometry based detection method for the mitochondrion-derived peptide MOTS-c in plasma samples for doping control purposes. Rapid Commun Mass Spectrom. 2019;33(4):371-380, PubMed
Certain bulk drug substances for use in compounding that may present significant safety risks, US Food and Drug Administration
Butré CI et al. Interlaboratory Evaluation of a User-Friendly Benchtop Mass Spectrometer. Molecules. 2023;28(6):2855, Molecules (PMC)
Erckes V et al. Towards a Consensus for the Analysis and Exchange of TFA as a Counterion in Synthetic Peptides. Pharmaceuticals. 2025;18(8):1163, Pharmaceuticals (PMC)
PubChem CID 146675088, MOTS-c, National Library of Medicine

Last reviewed 6 Oct 2026.