[The role of histidine residues of formate dehydrogenase from Bacterium sp. 1]

The reaction between formate dehydrogenase from Bacterium sp. 1 and diethylpyrocarbonate results in the enzyme inactivation. 4 histidine residues can be blocked per subunit by this reagent. The enzyme activity correlates with the disappearance of free histidines. The process of enzyme inactivation is biphasic and obeys pseudo-first-order kinetics. NAD and NADH slow down the rate of inactivation, but do not protect histidine residues against modification. Formate does not protect the enzyme. The modification of 80% of histidines increases the Km value for both substrates 3-fold. The general conformation of enzyme in the course of modification is preserved. The modification of histidines markedly decreases the reactivity of an essential SH-group of formate dehydrogenase against the Ellman reagent.