Aminotripeptidase of Swine Kidney

Abstract

Abstract The aminotripeptidase (tripeptidase:aminoacyl oligopeptide hydrolase, EC 3.4.1.3) of swine kidney has been isolated as three different homogeneous proteins that differ in chromatographic behavior, molecular weight, and in other properties. The enzyme is inactivated by certain sulfhydryl reagents and by some metal-chelating agents. Disulfide bonds are absent. Inactivation by the chelating agents can be reversed by the addition of certain metal ions. Although the enzyme contains zinc, the metal is not present in stoichiometric amount, and the role of this metal ion is unclear. Earlier and present studies of the specificity of the tripeptidase indicate that the enzyme does not hydrolyze di-, tetra-, or longer peptides, di- or tripeptide amides, or acyl peptides. Tripeptides with NH2-terminal glutamic or aspartic acids or with a central proline or hydroxyproline residue are resistant to hydrolysis. The enzyme is useful in ascertaining the sequence of tripeptides because of its rapid liberation of the NH2-terminal residue as the free amino acid. With longer peptides, it is convenient to remove one or more residues by the Edman degradation to leave the COOH-terminal tripeptide which can then be hydrolyzed by the enzyme. Phenylthiocarbamyl peptides or other products of the Edman procedure do not interfere with the hydrolysis of the residual free tripeptide.