Histidine residues and the enzyme activity of pig heart supernatant malate dehydrogenase

Abstract

1. Supernatant pig heart malate dehydrogenase is completely inhibited by reaction with diethyl pyrocarbonate at pH6.5, when 0.58±0.1 residue of ethoxycarbonylhistidine is formed per NADH-binding site. 2. Oxaloacetate and hydroxymalonate protect the enzyme from inhibition in the absence of coenzyme. 3. Limited ethoxycarbonylation does not alter the binding of NADH to the enzyme but prevents the enzyme–NADH complex from interacting with hydroxymalonate in a ternary complex.