The effect of x-rays on the level, composition and para-nitroanisole-o-demethylase activity of cytochrome P-450 in the liver microsomes of rats

A study was made of the effect of X-radiation of different doses on the content of P-450 cytochrome in a microsomal fraction of rat liver. When the haemoprotein level markedly decreased an increase in Km and a decrease in Vmax were noted in the reaction of O-demethylation of para-nitroanisole by microsomes of the irradiated rat liver. It is suggested that one of the cause of the effect observed is the postirradiation change in the composition of cytochrome P-450 pool resulting from a selective decrease in the level of the radiosensitive forms of haemoprotein.