Trypsin consists of a single chain polypeptide of 223 amino acid residues, produced by the removal of the N-terminal hexapeptide from trypsinogen which is cleaved at the Lys – lle peptide bond. The sequence of amino acids is cross-linked by 6 disulfide bridges. This is the native form of trypsin, beta-trypsin. BETA-trypsin can be autolyzed, cleaving at the Lys – Ser residue, to produce alpha-trypsin. Trypsin is a member of the serine protease family.