Chemical modification of the functional arginine residue(s) of malic enzyme from Zea mays

Abstract

Malic enzyme from Zea mays was modified with the arginine selective reagents, phenylglyoxal and 2,3-butanedione. The enzyme inactivation followed pseudo-first order kinetics with a half inactivation time of 3 min at 50 mM phenylglyoxal. NADP alone or in combination with Mg 2+ and substrate (malate) protected the enzyme against inactivation, suggesting that the arginine residue(s) are located at or near the active site of the enzyme. The phenylglyoxal-modified enzyme showed an affinity for NADPH like those of the native enzyme, while binding of l-malate was significantly reduced. These results indicate that the arginine residue(s) may be involved in binding of the carboxyl group of the substrate to the enzyme. Complete inactivation of the malic enzyme could be correlated with the incorporation of 4 mol [7- 14C]phenylglyoxal per mole of enzyme subunit and loss of two arginyl residues per subunit, of which one residue can be protected by NADP.