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

Abstract
The addition of p-nitroanisole to a reaction mixture containing rat liver microsomes caused an increase in 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-demethylation activity and the NADPH-dependent O-demethylation activity seen in rat liver microsomes. Addition of 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. Apparently NADH-dependent and NADPH-dependent O-demethylations are catalyzed by cytochrome P-448 and cytochrome P-450 receiving electrons from cytochrome b5.

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