Carboxypeptidase A usually refers to the pancreatic exopeptidase which hydrolyzes peptide bonds of C-terminal residues with aromatic or aliphatic side chains. Most scientists in the field now refer to this enzyme as CPA1, and to a related pancreatic carboxypeptidase as CPA2.
In addition, there are 4 other mammalian enzymes named CPA-3 through CPA-6, and none of these are expressed in the pancreas. Instead, these other CPA-like enzymes have diverse functions.
- CPA3 (also known as mast-cell CPA) is involved in the digestion of proteins by mast cells.
- CPA4 (previously known as CPA-3, but renumbered when mast-cell CPA was designated CPA-3) may be involved in tumor progression, but this enzyme has not been well studied.
- CPA5 and CPA6 have also not been well studied. Interestingly, a human mutation of CPA-6 is known to cause Duane's syndrome (abnormal eye movement). This, together with the localization of CPA-6 to embryonic eye muscle (in addition to other limited locations) suggests a role for CPA-6 in the control of neuronal migration/axonal guidance.
CPA-1 and CPA-2 (and presumably all other CPAs) contain a zinc atom at the active site. Loss of the zinc leads to loss of activity, which can be replaced easily by zinc, and also by some other divalent metals (cobalt, nickel).