The reaction of organophosphorus compounds with hydrolytic enzymes.: The inhibition of horse liver aliesterase

Abstract

Reaction rate constants were determined for the inhibition of horse liver aliesterase by a number of organophosphorus compounds with the general formula R 1R 2P(O)X at pH 7.7 and 25°. The influence of the structure of the groups R 1 and R 2 on the rate of inhibition is generally very small. The influence of the structure of the group X is much greater. There seems to be, however, only a slight correlation between the rate of the enzyme inhibition and the strength of the P—X bond. In two cases the influence of the temperature on the reaction rate was investigated. In both cases the activation enthalpy was found to be of the same order as in alkaline hydrolysis ; the activation entropy was very much higher than in the hydrolytic reactions. A colorimetric assay method for aliesterase is described.