Enzymatic Generation of Alloxan Radicals in Rat Liver Microsomes : Possible Participation of Reduced Nicotinamide Adenine Dinucleotide Phosphate (NADPH)-Cytochrome P-450 Reductase

Electron spin resonance studies showed that addition of rat liver microsomes to the reaction system of alloxan with reduced nicotinamide adenine dinucleotide phosphate (NADPH) resulted in a marked increase in the generation of alloxan radicals (AH・), whereas heat-denatured microsomes were without such effect. Oxidation of NADPH by alloxan was also stimulated by microsomes. The microsomes from rats treated with phenobarbital, an inducer of cytochrome P-450 reductase, greatly stimulated both the AH・ generation and the NADPH oxidation. However, the microsomes from rats treated with 3-methylcholanthrene, an inducer of DT-diaphorase, did not have stimulative effect greater than the control microsomes. These results suggest the possibility that NADPH-linked AH・ generations in microsomal membranes is catalyzed by NADPH-cytochrome P-450 reductase.