MOTS-c: a peptide encoded in the mitochondria

MOTS-c stands apart in this catalogue: the instructions for building it are not in the cell nucleus but in the mitochondria's own DNA. This article collects what can be documented about it.

Sixteen residues, two of them containing sulphur

The sequence is Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg, MRWQEMGYIFYPRKLR in one-letter code: sixteen amino acids. The molecular formula C₁₀₁H₁₅₂N₂₈O₂₂S₂ contains two sulphur atoms, which come from the two methionines at positions one and six.

The molar mass is 2174.60 g/mol and the CAS number 1627580-64-6. All of these figures are in the specification table on the product page.

Of the twenty standard amino acids, methionine is the most sensitive to oxygen. Two of them in a short chain are not an analytical footnote: if one oxidises, the mass rises measurably and mass spectrometry shows a second signal next to the expected one. That is why storage away from light and in the cold matters more here than for a chain without sulphur.

Instructions outside the nucleus

Mitochondria have their own DNA, a remnant of their history as independent cells. MOTS-c is encoded there, not in the nuclear genome. In in vitro research it is studied in connection with cellular metabolism, insulin signalling pathways and AMPK-dependent processes; what follows from this in a whole organism is the subject of ongoing research.

The other mitochondria-related molecule in this catalogue is SS-31, which takes a completely different route: it is not encoded there but directed there.

Five certificates, one clearly lower

The certificate library holds five certificates of analysis for this substance: three from 10 mg lots, the fill size sold here, and two from 40 mg lots. The measured purity is above 99.8%, 97.6% and 99.8% for the 10 mg lots, and 98.339% and 99.048% for the two 40 mg lots.

The 97.6% figure is below 98%. The certificate stays in the library, because a library from which the inconvenient figures disappear is no longer a library but advertising. What the difference between a promise and a measured value means is explained in How to read a certificate of analysis.

The 97.6% is not an isolated figure, incidentally: the same number appears for a lot of BPC-157. Both values come from the same laboratory and the same period.

What a mid-length chain means for manufacture

Sixteen residues mean fifteen coupling steps in solid-phase synthesis, clearly more than for the tetrapeptides in this catalogue and clearly fewer than for Retatrutide with 39. The share of incomplete chains that purification has to remove lies somewhere in between.

As for mass: 2174.60 g/mol is five times a short regulatory peptide and just under half of the long metabolic molecules. Purity should not be confused with peptide content, which is lower because of counterions and residual moisture.

Before preparing a solution

The product is supplied as a lyophilised powder; what lyophilisation does to the material is explained in Storing lyophilised peptides in the laboratory. It goes into solution with bacteriostatic water, and the glossary entries on reconstitution and concentration explain the terms.

In brief

Sixteen amino acids, 2174.60 g/mol, CAS 1627580-64-6, five certificates of analysis, three from the matching vial size and two from 40 mg lots, one of them at 97.6%, below its own specification.

Questions

What is special about MOTS-c?

Its building instructions are in the mitochondria's own DNA, not in the cell nucleus. Chemically, it is a chain of sixteen amino acids with two methionines.

Why does the library show values below 98%?

Because a measured value belongs to a single lot, and the library shows every certificate, including the inconvenient ones. One of the five reports 97.6%; it remains available to view.

Why is storage more delicate here?

Because of the two methionines. Of all the standard amino acids, methionine reacts most readily with oxygen, and oxidation changes the measurable mass.