Peptide sequence

The ordered chain of amino-acid residues that defines a peptide — the compound's actual identity, from which its formula, mass and behaviour follow.

A peptide is a chain of amino acids joined by amide bonds, and its sequence — which residues, in which order — is its definition. Two peptides with the same residues in different order are different compounds with different properties. Sequence is what a name like a five-letter code abbreviates, and it is the input from which theoretical molecular weight and formula are calculated.

Sequence also determines the properties that matter downstream: how many basic residues there are, and therefore how much counterion the salt form carries; which degradation pathways the molecule is prone to; and what mass an identity check should observe. When a certificate compares observed against theoretical mass, the theoretical side is computed from the sequence.

Modified residues complicate naming but not the principle. Many research peptides carry modifications — acetylation, amidation, unusual residues, fatty-acid side chains — and the modified sequence, not the parent one, is the compound's identity. This is one reason registry identifiers matter: two products sold under one trade name can differ in modification, and only sequence-level identity, checked by mass, distinguishes them.

For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice.