A possible role of cAMP dependent phosphorylation of hepatic microsomal cytochrome P450: a mechanism to increase lipid peroxidation in response to hormone.

Enzymatic lipid peroxidation in hepatocytes is believed to involve cytochrome P450. cAMP dependent phosphorylation of cytochrome P450 was found to increase the NADPH dependent production of malondialdehyde (lipid peroxidation) by about 30%. The cytochrome P450 inhibitor cyanide abolished this activity. The presence of spermine decreased the cytochrome P450 dependent lipid peroxidation in non-phosphorylated microsomes, phosphorylation partially reversed this effect. Thus, phosphorylation of cytochrome P450 and the associated increased lipid peroxidation may be a hormone dependent response to pathological conditions e.g. stress Phosphorylation was observed to subtly alter other properties of cytochrome P450. The rate of 7-ethoxycoumarin deethylase activity was reduced and the microwave power required to saturate the EPR spectrum of the low spin cytochrome P450 was decreased. It is hypothesized that phosphorylation of cytochrome P450 alters the interaction between the components of the cytochrome P450 system, which may enhance production of free radical species, initiating lipid peroxidation.