KINETICS OF THE INHIBITION OF α-CHYMOTRYPSIN BY METHANOL AND DFP

Abstract

A study has been made of the kinetics of the α-chymotrypsin-catalyzed hydrolysis of methyl hydrocinnamate in the presence of various concentrations of methanol, of eserine, and of diisopropyl phosphorofluoridate (DFP). In 20% methanol the pH optimum, using a substrate concentration of 1.20 × 10⁻³M, is 7.8; in pure water it is 8.3; and at intermediate pH's the optimum varies between these values. No inhibition was observed with eserine. In aqueous solution the character of the inhibition by DFP differs from that in alcohol solutions; the inhibition is of the competitive type, and the inhibition constant varies with pH in essentially the same manner as does the rate of the reaction. This result suggests that DFP interacts with the same active groups on the enzyme as are responsible for the hydrolysis of the substrate. A specific mechanism for inhibition is suggested.