Stability

Stability describes how far a peptide keeps its intended chemical and physical form over time under defined conditions. It never belongs to the molecule by itself: a statement about stability means nothing unless temperature, physical state, pH, container and light exposure are specified alongside it.

Five factors, ranked

Five factors dominate, listed approximately by how much they matter in practice. Physical state leads — a freeze-dried powder is stable by orders of magnitude longer than a solution, because the hydrolysis that cleaves peptide bonds requires water. Temperature follows, with reaction rates climbing sharply as things warm up. Third comes pH, because asparagine deamidation and aspartate isomerisation depend heavily on it. Fourth is the sequence itself: chains with methionine, cysteine or Asn-Gly motifs have well-known weak spots. Fifth is handling — light, air–water interfaces and repeated freeze–thaw transitions.

Stability is not the same as plasma half-life, which describes how enzymes and kidneys remove a peptide from a living organism. A peptide may keep perfectly in a freezer yet be cleared within minutes in the bloodstream; the two values answer separate questions. Confirming stability after a storage period requires a repeat HPLC run, not a look at the vial. See the storage guide and stability and half-life guide.

Related terms

degradation · cold chain · methionine oxidation