Tripeptidyl carboxypeptidase activity of kininase II (angiotensin-converting enzyme)

The degradation of des-Arg⁹-bradykinin and its analogues by highly purified preparations of hog lung and kidney kininase II (angiotensin-converting enzyme; peptidyldipeptide hydrolase, EC 3.4.15.1) was studied. The degradative peptide fragments were separated and isolated by high performance liquid chromatography and identified by amino acid analysis. Both enzymes released C-terminal tripeptides from des-Arg⁹-bradykinin, des-Arg⁹-(Leu⁸)-bradykinin, Pro-Pro-Gly-Phe-Ser-Pro-Phe, Pro-Gly-Phe-Ser-Pro-Phe, Gly-Phe-Ser-Pro-Phe, Bz-Gly-Ser-Pro-Phe and Bz-Gly-Ala-Pro-Phe. Hydrolysis of Phe-Ser-Pro-Phe, Bz-Gly-His-Pro-Phe, Bz-Gly-Phe-Pro-Phe and Bz-Gly-Gly-Pro-Phe by both enzymes was negligible. These data indicate that kininase II can release C-terminal tripeptides of substrates having a proline residue in the penultimate position such as des-Arg⁹-bradykinin and its analogues, and that this enzyme is able not only to act as a dipeptidyl carboxypeptidase but also acts as a tripeptidyl carboxypeptidase. The tripeptidyl carboxypeptidase activity of this enzyme was sensitive to inhibition by kininase II inhibitors.