Interactions between solubilized cytochrome P-450 and hepatic microsomes.

Solubilized cytochrome P-450 has been prepared from the livers of 3-methylcholanthrene-pretreated rats. The enzyme preparation does not catalyze the monoxygenase reactions unless NADPH-cytochrome P-450 reductase and phospholipids are also present. Addition of solubilized cytochrome P-450 to rat liver microsomes increases the NADPH-dependent benzpyrene hydroxylase activity. The extent of the enhancement in catalytic activity is proportional to the amount of exogenous cytochrome P-450 bound to the microsomes. The microsomal bound exogenous cytochrome P-450 can be enzymically reduced and hence is capable of catalyzing the oxygenation of benzpyrene. The addition of solubilized cytochrome P-450 also enhances the NADH-supported microsomal benzpyrene hydroxylation and the NADH synergism of the NADPH-supported reaction. It is proposed that the added cytochrome P-450 can be incorporated into the membrane and become a functional part of the microsomal monoxygenase system.