Abstract

Liver arginase from Genypterus maculatus was completely inactivated by Woodward's reagent K (WRK) and partially inactivated by diethyl pyrocarbonate (DEPC). Borate protected against inactivation by DEPC and caused a nontotal inhibition of the enzyme. Inactivation by WRK (second order rate constant, 26.3 M-1 min-1) was associated to the chemical modification of a single residue with a pK(a) value of 6.5 at 25°C. Inactivation by DEPC (second order rate constant, 336 M-1 min-1) involved a single residue with a pK(a) of 6.8 at 25°C and it was reversed by hydroxylamine. A carboxylate residue associated to the action of a metal-bound hydroxyl as a nucleophile, and a histidine residue with a nonessential role in the catalytic mechanism of arginase, are considered.