Carboxypeptidase A1 is an enzyme that in humans is encoded by the CPA1 gene. Three different forms of human pancreatic procarboxypeptidase A have been isolated. The A1 and A2 forms are monomeric proteins with different biochemical properties. Carboxypeptidase A1 is a monomeric pancreatic exopeptidase. It is involved in zymogen inhibition. Carboxypeptidase B (EC 3.4.17.2, protaminase, pancreatic carboxypeptidase B, tissue carboxypeptidase B, peptidyl-L-lysine [L-arginine]hydrolase) is a carboxypeptidase that preferentially cleaves off basic amino acids arginine and lysine from the C-terminus of a peptide. This enzyme is secreted by the pancreas, and it travels to the small intestine, where it aids in protein digestion. Plasma carboxypeptidase B (carboxypeptidase B2) is responsible for converting the C5a protein into C5a des-Arg, with one less amino acid.