Abstract
Following the previous study on deethylation of p-nitrophenetole with rabbit liver microsomes, demethylation of p-nitroanisole was analogously investigated, using reduced nicotinamide adenine dinucleotide (NADH), reduced nicotinamide adenine dinucleotide phosphate (NADPH) and NADH plus NADPH as the cofactor. It was found that this reaction proceeded well with NADH as well as NADPH, and this NADH-dependent demethylation was different from those of other two systems. For example, optimum pH was 6.0 in the NADH system, but was 7.4 in the NADPH or NADH plus NADPH system, and the reaction was inhibited by CO in the NADPH or NADH plus NADPH system, but not in the NADH system. Furthermore, KCN did not inhibit the demethylation in any one of three systems at 10-4M. These results were just the same as obtained in the deethylation of p-nitrophenetole and suggested also a possible involvement of a new type of NADH-dependent oxygenase which was different from cytochrome P-450 and cyanidesensitive factor, in the demethylation of p-nitroanisole with rabbit liver microsomes. The NADPH-and NADH plus NADPH-dependent demethylations, on the other hand, were assumed to be catalyzed by the enzyme system involving cytochrome P-450.
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