Ethanol Oxidation by a Component of Liver Microsomes Rich in Cytochrome P-450

A cytochrome P-450-rich fraction free of alcohol dehydrogenase activity and containing only small amounts of catalase was prepared from rat liver microsomes and shown to catalyze the NADPH-dependent oxidation of ethanol. The recoveries of cytochrome P-450 and the activity of the NADPH-dependent ethanol oxidation were 15.6% and 14.0%, respectively. The addition of separated cytochrome c reductase to the cytochrome P-450 fraction resulted in an increase in the ethanol-oxidizing activity, while the addition of microsomal lipid had a mild inhibitory effect on the activity catalyzed by the combined cytochrome P-450 and cytochrome c reductase fractions. Substitution of the NADPH-generating system by a system generating H2O2 also resulted in oxidation of ethanol by the cytochrome P-450-rich fraction, although at a slightly slower rate. The separated catalase fraction oxidized ethanol only in the presence of a system generating H2O2. It is concluded that ethanol oxidation can be catalyzed by a microsomal component rich in cytochrome P-450 and separate from contaminating alcohol dehydrogenase and catalase.