The journal
What actually degrades a peptide
“Store cold, keep it dry, keep it dark” is good advice and a poor explanation. Peptides do not degrade generically; they degrade by specific chemical routes, and which routes are open depends on which residues are in the sequence. Knowing the mechanism tells you which of your vials is fragile and which is nearly indestructible.
Oxidation
Three residues are vulnerable to oxygen: methionine above all, then cysteine and tryptophan. Methionine's sulphur picks up an oxygen to become the sulphoxide, adding sixteen daltons — which is exactly why mass spectrometry catches it.
In this catalog that means Semax (one methionine), MOTS-c (two, plus a tryptophan) and tesamorelin (one) are the compounds where headspace air and open solutions matter most. Melanotan II carries a tryptophan and is photosensitive for the same family of reasons.
Mitigation: minimise the air in the vial, keep it closed, do not leave solutions standing open, and keep them dark.
Deamidation
Asparagine and, more slowly, glutamine lose their side-chain amide and become the corresponding acid. The mass changes by one dalton — a small number that a good mass spectrometer sees clearly and a purity percentage may not.
Asparagine followed by glycine is the fastest case of all, because the reaction proceeds through a cyclic intermediate that a small neighbouring residue makes easy. Rate rises sharply with pH and with temperature.
Mitigation: neutral to slightly acidic conditions, and cold.
Hydrolysis
The peptide bond itself can be cleaved by water, most readily where an aspartate sits next to a proline. Acidic conditions and heat both accelerate it.
BPC-157 is worth noting here: it contains Asp-Asp-Ala and a great deal of proline. Not a fragile peptide by any standard, but the chemistry is present.
Disulphide scrambling
Only relevant where a molecule has more than one disulphide bond, and in this catalog that means IGF-1 LR3, which has three. Under mildly alkaline or reducing conditions those bonds can break and re-form in the wrong pairings. The mass does not change at all. The molecule is no longer the same molecule.
This is the degradation route that neither instrument on a standard certificate reports well, and it is why the folded protein in the catalog is the one handled most carefully.
Aggregation
Not chemistry but physics: molecules associating with one another and coming out of solution. Driven by agitation, by freeze-thaw cycling, and by concentration. Once it has happened it does not reverse on standing.
This is the mechanism behind the two rules that sound like superstition and are not: never shake a vial, and never freeze and thaw the same solution twice.
Why the dry state is so much safer
Every route above except aggregation needs water to proceed. Oxidation is accelerated by it, deamidation requires it, hydrolysis is it. Lyophilisation removes it.
That is the whole reason these compounds ship as a freeze-dried cake rather than a solution, and it is why a lyophilised powder at −20 °C is stable for months to years while the same material in solution is measured in days to weeks. The moment you reconstitute, you have started a clock that was not previously running.
The practical short list
- Powder at −20 °C, dry, dark, sealed.
- Equalise to room temperature before opening, so condensation does not form on the powder.
- In solution: refrigerate, keep dark, and treat the working life as short.
- Aliquot before freezing, never after. One thaw per aliquot.
- Avoid alkaline buffers unless the protocol requires them.
- Label everything with compound, lot, concentration and date.
Per-compound notes — which residues each molecule contains and what that implies — are in the compound reference. The vial label and the certificate always govern where they differ from general guidance.
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