Kinetics of the hydrolysis of benzoylglycine ethyl ester catalyzed by papain

The hydrolysis of benzoylglycine ethyl ester has been investigated. The kinetics can be described by the conventional Michaelis-Menten scheme. The substrate appeared to be only four times less sensitive than the best known substrate benzoylarginine ethyl ester. The pH dependence of the hydrolysis of benzoylglycine ethyl ester closely resembled equivalent data for other papain (EC 3.4.4.10) substrates as reported in the literature. The binding of the substrate was maximal at pH 6, half-maximal at pH 4 (ascribed to a carboxyl group in the active centre) and at pH 8 (ascribed to a sulfhydryl group or an imidazolium group). The vmax was constant in the range pH 4.2–8.4 , which indicates that histidine is not involved in the catalytic step as it is with trypsin (EC 3.4.4.4) and chymotrypsin (EC 3.4.4.5). The experimental procedure is described in detail. The purity of the papain was checked by chromatography on a CM-cellulose column, and by electrophoresis in starch gel.