NAD (P) H-dependent reduction of nicotinamide N-oxide by an unique enzyme system consisting of liver microsomal NADPH-cytochrome c reductase and cytosolic aldehyde oxidase

Abstract

NAD(P) H-dependent reduction of nicotinamide N-oxide was investigated with rabbit liver preparations. Microsomes, microsomal NADPH-cytochrome c reductase or cytosolic aldehyde oxidase alone exhibited no nicotinamide N-oxide reductase activity in the presence of NADPH or NADH. However, when the microsomal preparations were combined with the cytosolic enzyme, a significant N-oxide reductase activity was observed in the presence of the reduced pyridine nucleotide. The activity was enhanced by FAD or methyl viologen. Cytosol alone supplemented with NADPH or NADH exhibited only a slight, but when combined with microsomes, a significant N-oxide reductase activity. Based on these facts, we propose a new electron transfer system consisting of NADPH-cytochrome c reductase and aldehyde oxidase, which exhibits nicotinamide N-oxide reductase activity in the presence of the reduced pyridine nucleotide.