Hydrolysis of Anhydrides by Esterases

Abstract

IN recent investigations¹ the idea was expressed that tetraethyl pyrophosphate and related inhibitors of esterases are enzymatically split into a positive phosphonium ion and a negative residue, the former attaching itself to a nucleophilic group in the active surface of the enzyme. The irreversible combination of organic phosphates with esterases is thus analogous to the reaction of esters as substrates: here the acylinium ion is attached reversibly to the enzyme. The ease with which anhydride bonds are split was used for explaining the superiority of this type of inhibitor over trialkyl phosphates. However, since esters are the natural substrates of esterases, it can be expected that both types of compounds, esters as well as anhydrides, are attacked by the same enzyme, the latter at a faster rate. This was borne out by the following experiments.