Definition
The ordered list of amino acids in a peptide, written from the N-terminus to the C-terminus.
A peptide's amino acid sequence is the order of its residues, written from the N-terminus to the C-terminus in three-letter (Gly-Glu-Pro) or one-letter (GEP) code. The sequence defines the theoretical molecular weight used for mass spectrometry, the net charge that guides solvent choice, and the residues that limit stability, such as methionine and cysteine for oxidation or asparagine for deamidation. Research peptides often contain modifications outside the 20 standard amino acids: D-amino acids, aminoisobutyric acid (Aib), N-terminal acetylation, C-terminal amidation or fatty-acid chains. A certificate of analysis should state the full sequence, including every modification.