Carboxypeptidase A1 (CPA1) is secreted as a pancreatic peptidase that comes from the precursor form of inactive procarboxypeptidase. CPA1 comprises a signal peptide, a pro region and a mature chain, and can be activated after cleavage of the pro peptide. It has a free C-terminal carboxyl group, with the preference of residues with aromatic or branched aliphatic side chains. CPA1 cleaves the C-terminal amide or ester bond of peptides and involves in zymogen inhibition. Three different forms of human pancreatic procarboxypeptidase A have been isolated. In contrast to procarboxypeptidase B which was always secreted by the pancreas as a monomer, procarboxypeptidase A occurs as a monomer and/or associated to one or two functionally different proteins, such as zymogen E.