MOTS-c is a 16-residue peptide encoded in the 12S rRNA region of the mitochondrial genome. This article covers only its chemistry, analysis and handling: what the sequence implies for stability, what a certificate of analysis can and cannot show about identity, and how to keep the material intact on the bench. PepXtide supplies it for laboratory research use only; not for human consumption.
Sequence and structure
The one-letter sequence is MRWQEMGYIFYPRKLR. The peptide is linear, and unless the certificate states a modification, the termini are free: a primary amine at the N-terminus and a carboxylic acid at the C-terminus.
Three residues matter most for stability. Methionine occurs at positions 1 and 6, and tryptophan at position 3. Methionine thioether groups oxidise readily to the sulfoxide, and the indole ring of tryptophan is also vulnerable to oxidation. Both reactions can proceed slowly in the solid state and faster in solution, particularly with air and light exposure.
Charge is set by the basic residues: arginine at positions 2, 13 and 16, and lysine at position 14. Against one glutamate at position 5, these give the peptide a strongly positive character at neutral pH. This affects how it behaves on reversed-phase columns, how it adsorbs to some plastics and glass, and which charge states appear in electrospray mass spectra.
Formula and mass: take them from the certificate
The molecular formula, average mass and monoisotopic mass for a given vial should be read from the product certificate rather than from a general table. The comparison that matters is between the mass the report lists as expected and the mass the laboratory observed. If a certificate does not list a value, nothing should be inferred from other sources.
What identity confirmation looks like
A certificate typically contains two kinds of data. An HPLC trace, measured against a reference standard, shows the main peak and its relationship to other peaks. LC-MS shows whether the main peak has the expected mass and the expected series of charge states. Each report reflects what one laboratory measured on one sample. Testing is done by a third party, named on each report, and some certificates may still be pending.
Mass spectrometry is the stronger identity evidence because it reports mass directly. Published work on MOTS-c shows that LC-MS detection of this peptide in a complex matrix is achievable (PMID: 30394592), and the wider analytical literature on emerging peptide compounds treats mass spectrometry as the reference approach (PMID: 26842585).
Oxidation peaks and breakdown fragments
A peak at +16 Da relative to the intact mass usually indicates one added oxygen, most often a methionine sulfoxide, though oxidised tryptophan gives the same shift. A +32 Da peak points to two such oxidations. Because MOTS-c has two methionines and a tryptophan, these species are the first thing to look for when the spectrum shows more than the intact ion.
LC-MS methods for this peptide track oxidation products and breakdown fragments separately from the intact peptide. Each is monitored as its own species, so a small oxidised population is not hidden inside the main signal. When reading a report, check whether such species are listed, and compare their retention times with the main peak, since oxidised forms often elute slightly earlier on reversed-phase columns.
Why an ELISA number is not proof of identity
An immunoassay detects an epitope, not a molecule. An antibody may bind an oxidised form, a truncated fragment or a related sequence, so the signal can reflect more than the intact peptide. This is why an ELISA value can disagree with an LC-MS result on the same material. ELISA can be useful as a supporting measurement, but identity rests on mass and chromatographic data. If the two disagree, the mass spectrum is the better guide to what the sample contains.
Storage and bench handling
Keep the lyophilised powder cold, dry and dark. Limit exposure to air and light, because those drive oxidation of the two methionines and the tryptophan. Allow the sealed vial to reach room temperature before opening, so that condensation does not wet the powder.
Prepare a stock solution for assay just before it is needed, in a solvent and at a concentration suited to the downstream method. Divide the stock into single-use aliquots and avoid repeated freeze-thaw cycles. Low-binding tubes can reduce losses of this basic peptide to surfaces.
For traceability, record the certificate's Report ID or Laboratory ID and the certificate date alongside the date the vial was opened and each aliquot was prepared. These records make it possible to match any later result to the analytical data for that material.
As above, this material is for laboratory research use only; not for human consumption.
For research use only. This guide covers bench handling of laboratory research materials. It does not describe an application, benefit, dose, route or outcome, and nothing in it is guidance for use in a person or an animal. Nothing sold by PepXtide has been evaluated by the FDA.
Where this applies on the site
The certificate library
Every published certificate, scanned as the laboratory issued it.
Quality control
The method, the laboratory, and the real spread of results.
MOTS-c
Named in this guide. Metabolic Research.
GHK-Cu
Has a published certificate to read against this guide.
GLP-2 (Tirzepatide) 20mg
Has a published certificate to read against this guide.
Tesamorelin
Has a published certificate to read against this guide.