THE INVOLVEMENT OF CYTOCHROME P-448 AND P-450 IN NADH-DEPENDENT O-DEMETHYLATION OF p-NITROANISOLE IN RAT LIVER MICROSOMES

Abstract

These studies have shown that addition of p-nitroanisole to a reaction mixture containing rat liver microsomes resulted in an increase the reoxidation rate of NADH- reduced cytochrome b5. Fortification of rat liver microsomes with partially purified cytochrome b5 produces an increase in both NADPH-dependent and NADH-dependent p-nitroanisole O-demethylation activity. Antiserum to cytochrome P-450 isolated from phenobarbital-treated rat liver microsomes inhibited the NADH-dependent O-deme-thylation activity as well as the NADPH-dependent O-demethylation activity seen in rat liver microsomes. Addition of either purified cytochrome P-450 or cytochrome P-448 to an incubation mixture containing phenobarbital-treated rat liver microsomes enhanced the NADH-dependent p-nitroanisole O-demethylation activity. These results suggest that NADH-dependent and, in part, NADPH-dependent O-demethyl- ations are catalyzed by cytochrome P-448 and cytochrome P-450 receiving electrons from cytochrome b5.