Modification of arginine residues of pea lactate dehydrogenase by phenylglyoxal

Abstract

Electrophoretically homogeneous lactate dehydrogenase was isolated from germinating pea seedlings by chromatography on AMP-Sepharose 4B. The amino acid composition of the enzyme was determined as well as the values of the Michaelis constants for four substrates and of the dissociation constants for the binary enzyme-coenzyme complexes. The treatment of the enzyme with phenylglyoxal resulted in the modification of nine arginine residues in its subunit. The modification was paralleled by a complete inactivation of the enzyme. The role of the arginine residues in the active center probably involves the binding of substrates, lactate and pyruvate, to the apoenzyme by an ionic bond.