Carboxypeptidases are proteolytic enzymes that remove L -amino acids, one residue at a time, from the carboxyl terminus of polypeptide chains, i.e., they are exoproteases. A number of such enzymes have been isolated from plant and animal sources, each differing in their chemical and physical properties and the rate at which they release particular amino acids. The major use of carboxypeptidases in molecular biology is in the determination of the C-terminal amino acid sequence of peptides and proteins (no suitable chemical method exists for the sequential removal of C-terminal amino acids from a polypeptide). The protein or peptide being analyzed is digested with carboxypeptidase and aliquots removed at timed intervals, and analyzed for the presence of free amino acids. The amount of each amino acid released is plotted against time, and the C-terminal sequence deduced from the relative rate of release of each amino acid. Four carboxypeptidases have been used extensively to provide peptide and protein sequence data. These are: carboxypeptidase A (EC 3.4.17-l) from bovine pancreas (1 ), carboxypeptidase B (EC 3.4.17.2) from porcine pancreas (1 ), carboxypeptidase C (EC 3.4.12.1) from orange leaves (2 ), and carboxypeptidase Y (EC 3.4.16.1) from yeast (3 ). Historically, carboxypeptidases A and B were the first to be discovered and used for sequence determination.
