[Inactivation of cytochrome P-450 in hydroxylase reactions]

It has been shown that sodium azide, a catalase inhibitor, accelerates the inactivation of cytochrome P-450 in reactions of hydroxylation of type I substrates, e.g., dimethylaniline (DMA), aminopyrine (AP), benzphetamine (BPh), p-nitroanisole (p-Na) and type II substrates--aniline (AN). In the absence of sodium azide, cytochrome P-450 is either non-activated (as in the case of AN) or is inactivated at a low rate. Haemoprotein inactivation in the presence of sodium azide in all hydroxylation reactions with the exception of O-demethylation of p-NA is a first-order reaction with respect to cytochrome P-450. Studies on the mechanism of cytochrome P-450 inactivation demonstrated that hydrogen peroxide formed via the NADPH-dependent hydroxylase cycle exhibits an inactivating effect towards the enzyme. The value of inactivation constant for cytochrome P-450 in hydroxylation reactions proceeding in the presence of sodium azide coincides with that of enzyme inactivation in the NADPH-oxidase and glucose oxidase systems generating H2O2.