Carboxypeptidases (CP) are zinc-containing exopeptidases that remove single amino acids from the carboxyl end of oligopeptides, many of which resulted from digestion of dietary proteins by pepsin, trypsin and chymotrypsin.
Carboxypeptidases are involved in a wide range of physiological processes, ranging from the digestion of food to the biosynthesis of peptides that function in cell-cell signaling. There are two major groups of carboxypeptidases; one uses serine as an active site residue and the other uses zinc in the active site Barrett et al (1998a), Barrett et al (1998b). The Serine and metallocarboxypeptidases do not share any amino acid sequence identity. The metallocarboxypeptidase family can be further divided into two subgroups based on amino acid sequence similarities. Each group has approximately 40–60% amino acid sequence identity with other members of the same group, but only 15–25% amino acid sequence identity with members of the other group. Each member of the metallocarboxypeptidase family can also be classified based on the substrate specificity: enzymes selective for C-terminal aromatic or aliphatic residues (CPA1, CPA2, CPA3, CPA5, and presumably CPA4 and CPA6—the activity of these two have not been reported); enzymes selective for C-terminal basic residues (CPB1, CPB2, CPD, CPE, CPM, CPN, and CPZ); enzymes presumably selective for C-terminal acid residues (CPO—the activity of this protein has not been reported); and carboxypeptidase-like proteins that lack one or more of the critical active site residues and that are not active as carboxypeptidases (AEBP1, CPX1, and CPX2).
