Hydrolysis of Amino‐Acid Esters by Pig‐Pancreatic Kallikrein

Abstract

Initial velocities of the hydrolysis of α‐N‐acylated esters of 14 different amino acids catalyzed by pig pancreatic kallikrein were determined. Control experiments with kallikrein partially inactivated by controlled treatment with diisopropylphosphorofluoridate demonstrated the enzymic homogeneity of the preparation and the ability of kallikrein to hydrolyse (at decreasing rates) esters of basic, aromatic and neutral aliphatic amino acids, though being predominantly specific for l‐arginine esters. The controversial literature on the substrate specificity of the enzyme has its origin not in the molecular heterogeneity of kallikrein, but in a contamination with other enzymes. Kinetic constants for the kallikrein‐catalyzed hydrolysis of several of the esters have been determined and compared to those of trypsin and clostripain. The preference of kallikrein for an arginine over a lysine ester is still higher than with the latter enzyme. In the α‐N‐benzoylated as well as in the α‐N‐tosylated series, esters of l‐arginine with different alcohol moieties exhibit not only widely different Km, but also Kcat values. The latter parallel the rates of the hydroxyl‐ion‐catalyzed hydrolyses of the α‐N‐benzoyl‐l‐arginine esters which have also been determined.Syntheses of α‐N‐benzoyl‐l‐lysine methyl ester hydrochloride and of α‐N‐benzoyl‐l‐ornithine methyl ester hydrochloride are described. A value for the rate constant of the hydroxyl‐ion‐catalyzed lactamization of the ornithine ester has been obtained.