Cytochrome P-450 enzyme-specific control of the regio- and enantiofacial selectivity of the microsomal arachidonic acid epoxygenase

Chiral analysis of the rat liver microsomal arachidonic acid epoxygenase metabolites shows enantioselective formation of 8.9-, 11,12-, and 14,15-cis-epoxyeicosatrienoic acids in an approximately 2:1, 4:1, and 2:1 ratio of antipodes, respectively. Animal treatment with the cytochrome P-450 inducer phenobarbital increased the overall enantiofacial selectivity of the microsomal epoxygenase and caused a concomitant inversion in the absolute configurations of its metabolites. These effects of phenobarbital were time-dependent and temporally linked to increases in the concentration of microsomal cytochrome P-450 enzymes. Reconstitution of the epoxygenase reaction utilizing several purified cytochromes P-450 demonstrated that the asymmetry of epoxidation is under cytochrome P-450 enzyme control. These results established that the chirality of the hepatic arachidonic acid epoxygenase is under regulatory control and confirm cytochromes P-450 IIB1 and IIB2 as two of the endogenous epoxygenases induced in vivo by phenobarbital.