Inactivation of Phosphoenolpyruvate Carboxylase from Maize Leaves by Modification with Phenylglyoxal

A.A. IGLESIAS, D.H. GONZÁLEZ, C.S. ANDREO

BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS

Año: 1984 vol. 788 p. 41 - 47

0304-4165

Phenylglyoxal rapidly and completely inactivated maize leaf phosphoenolpyruvate carboxylase. Inactivationexhibited pseudo-first-order kinetics with a reaction order of approximately one and a second-order rateconstant of 8.32 mM-1. min-t. Phosphoenolpyruvate, and more effectively phosphoenolpyruvate plusMgCI 2, protected the enzyme against inactivation, suggesting that the modification occurs at or near to thesubstrate-binding site. Malate and oxalacetate also prevented inactivation. The protective effects of phosphoenolpyruvate(in the absence or in the presence of MgCl 2) and malate were studied at pH 7.0, 7.5 and7.9. In the absence of MgCI 2, phosphoenolpyruvate was more effective at pH 7.5, while in the presence ofMgCi 2 the protection increased along with the pH. On the other hand, in the absence of MgCI 2, malate atpH 7 afforded higher protection than phosphoenoipyruvate. Loss of enzymic activity was directly proportionalto the incorporation of [2-t4Clphenyiglyoxal at least until 30% of the initial activity remained.Complete inactivation of the carboxylase was correlated with the incorporation of 8 tool [2-14 C]phenyiglyoxalper tool enzyme. When phosphoenolpyruvate plus MgCI 2 were used as protective agents, this numberreduced to 4. Assuming a stoichiometry of 2:1 between phenylglyoxai incorporation and arginine modification,these results suggest that only two arginine residues per phosphoenolpyruvate carboxylase molecule areresponsible for inactivation.