Binding of peptide substrates and inhibitors of angiotensin-converting enzyme. Importance of the COOH-terminal dipeptide sequence.

Among three biologically active substrates of angiotensin-converting enzyme, enzyme-binding affinities increase and chloride ion rate enhancements decrease in the following order: angiotensin I (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu), bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg), bradykinin-potentiating peptide 5, (<Glu-Lys-Trp-Ala-Pro).Qualitatively simil a r properties are observed a m o n g the much simpler tripeptide substrates, Hip-His-Leu, Hip-Phe-Arg, and Hip-Ala-Fro, that have the same COOH-terminal dipeptides as the larger substrates.The s a m e order of enzyme-binding affinities is also found with competitive dipeptide inhibitors, His-Leu, Phe-Arg, and Ala-Pro.Such results suggest that selective binding of the COOH-terminal dipeptide residue is an important determinant of both the substrate specificity of angiotensin-converting enzyme and the degree of rate stimulation by chloride ion, and that the nature of this selective binding can be further clarified by studying competitive inhibition b y dipeptides of varying structure.NH2-terminal glycyl dipeptides v a r y 300-fold in inhibitory potency, those with tryptophan, tyrosine, or proline being the most inhibitory.COOH-terminal glycyl dipeptides vary only 16-fold in inhibitory activity, with valine, isoleucine, and arginine as the most effective NHz-terminal residues.The most potent dipeptide tested, Val-Trp (& = 0.3 pM), was 10,000 times more inhibitory than the weakest inhibitor Pro-Gly, suggesting that angiotensin-converting enzyme is highly specific with regard to the terminal dipeptide residues of peptide substrates or competitive inhibitors.Inhibitory potencies of dipeptides also correlate with the inhibitory potencies of structurally analogous, but nonpeptidic, mercaptopropanoyl amino acids related to the antihypertensive drug captopril (SQ 14,225), as predicted from a hypothetical model of the active site of angiotensin-converting enzyme.Angiotensin-converting enzyme (peptidyldipeptide hydrolase, EC 3.4.15.1) is an unusual dipeptide-liberating exopeptidase that plays a key physiological role in the regulation of blood pressure by virtue of two different reactions that it catalyzes: conversion of the inactive decapeptide angiotensin I to a powerful vasoconst.rictorand salt-retaining octapeptide, angiotensin 11, and inactivation of the vasodilator and natri-* A preliminary report of this work was presented at the 62nd Annual Meeting of the Federation of Societies for Experimental Biology, April 9 to 14, 1978, Atlantic City, N. J.The costs of publication of this article were defrayed in part by the payment of page charges.This article must therefore be hereby marked "aduertisement" in accordance with 18 U.S.C.Section 1734 solely to indicate this fact.' The abbreviations or other designations used are: BPPs., bradykinin-potentiating peptide 5. (tGlu-Lys-Trp-Ala-Pro); SQ 14,225, captopril (~-3-mercapto-2-methylpropanoyl-~-proline); SQ 20,881, te