Carboxypeptidase A (CPA) is a pancreatic exopeptidase which hydrolyses the peptide bond adjacent to the C-terminal end in polypeptide chains. Mast cell carboxypeptidase A (MC-CPA), a part of the peptidase M14 family, is a highly conserved metalloprotease localized to the secretory granules, along with trytases and chymases. MC-CPA is stored as an active enzyme in the granule and is released, along with other inflammatory mediators, upon mast cell degranulation. MC-CPA mirrors pancreatic carboxypeptidase A in cleaving COOH-terminal aromatic and aliphatic amino acid residues. The optimum pH of MC-CPA is between neutral and basic, depending upon the substrate. The MC-CPA gene, CPA3, resides on chromosome 3 and contains 11 exons.