Carboxypeptidase A usually refers to the pancreatic exopeptidase that hydrolyzes peptide bonds of C-terminal residues with aromatic or aliphatic side-chains.

CPA-1 and CPA-2 (and, it is presumed, all other CPAs) employ a zinc ion within the protein for hydrolysis of the peptide bond at the C-terminal end of an amino acid residue.

Carboxypeptidase A is produced in the pancreas and is crucial to many processes in the human body to include digestion, post-translational modification of proteins, blood clotting, and reproduction.

This vast scope of functionality for a single protein makes it the ideal model for research regarding other zinc proteases of unknown structure.

Recent biomedical research on collagenase, enkephalinase, and angiotensin-converting enzyme used carboxypeptidase A for inhibitor synthesis and kinetic testing.

This allowed for a potent carboxypeptidase A inhibitor to be used to inhibit the enzyme and, thus, lower blood pressure through the renin-angiotensin-aldosterone system.

Stabilization of both the coordinated water molecule and negative intermediates are assisted by polar residues in the active site which are in close proximity to facilitate hydrogen bonding.

[2] The hydrogen bonding from the hydroxyl group in Tyr-248 facilitates this conformation due to interaction with the terminal carboxylates of substrates that bind.

A triad of residues interact to the C-terminal carboxylate through hydrogen bonding: Classified as a metalloexopeptidase, carboxypeptidase A consists of a single polypeptide chain bound to a zinc ion.

This characteristic metal ion is located within the active site of the enzyme, along with five amino acid residues that are involved in substrate binding: Arg-71, Arg-127, Asn-144, Arg-145, Tyr-248, and Glu-270.

A plane exists that bisects the active-site groove where residues Glu-270 and Arg-127 are on opposite sides of the zinc-water coupled complex.

In 1934, it was first discovered through kinetic experiments that, in order for substrate to bind, the peptide that is to be hydrolyzed must be adjacent to a terminal free hydroxyl group.