BENZYL VIOLOGEN INACTIVATION OF RAT-LIVER GLUTAMINE-SYNTHETASE

Partially purified glutamine synthetase from rat liver underwent rapid inactivation upon incubation with NADH and benzyl viologen, under aer obic conditions. This in vitro inactivation was prevented by catalase or chelating-agents, which suggests that hydrogen peroxide and metal i ons are involved in the process. Similar inactivation was observed whe n the rat liver glutamine synthetase was preincubated, under anaerobic conditions, with NADH and benzyl viologen, and hydrogen peroxide was added to the reaction mixture. A radical se-avenger, histidine, partia lly prevents the inactivation, while hydrogen peroxide shows a low ina ctivation capacity when incubated without NADH. Furthermore, the fact that the inactivation can also be catalyzed by a model consisting of f errous ions and hydrogen peroxide leads to the conclusion that hydroxy l radicals, or something with similar reactivity, are most likely prod uced through a Fenton reaction.