Analysis of the effects of inhibitors on NADPH-dependent electron transport in rat liver microsomes

Abstract

Analysis of the effects of inhibitors on NADPH-oxidation in rat liver microsomes shows that the rate of total oxygen consumption parallels the rate of peroxidation of unsaturated fatty acids but not the rate of electron transfer within the chain. The addition of EDTA, 1 mM, to the incubation medium inhibits peroxidation and does not affect NADPH-dependent electron transfer. There are at least three sites for oxygen reduction within the NADPH-oxygenase complex. Oxygen reduction in the chain may occur both at the flavoprotein level and at the level of cytochrome P-450. In addition, Fe 2+ ions bound with the functional groups of electron carriers and catalyzing the peroxidation of unsaturated fatty acids also participate in oxygen reduction. The fact that there are several points of activation of molecular oxygen within the NADPH-dependent electron transport chain precludes the evaluation of the effectiveness of action of inhibitors on cytochrome P-450 by measurement of the total oxygen consumption. NADH oxidation inhibited by EDTA is activated by addition of Ca 2+.