title: Participation of a rat liver cytochrome P-450 induced by pregnenolone 16 alpha-carbonitrile and other compounds in the 4-hydroxylation of mephenytoin.
abstract: Mephenytoin 4-hydroxylation, which has been found to be one of the reactions showing genetic polymorphism in humans, has been studied using rat liver microsomes. Pregnenolone 16 alpha-carbonitrile, dexamethasone, troleandomycin, and phenobarbital (but not beta-naphthoflavone) induced the hydroxylation activity to various extents. Mephenytoin itself also increased 4-hydroxylation considerably. Liver microsomes prepared from male rats contained higher mephenytoin hydroxylase activity than preparations isolated from females. These results suggest that a cytochrome P-450 which is inducible by pregnenolone 16 alpha-carbonitrile is involved in the 4-hydroxylation of mephenytoin. We purified cytochrome P-450PCN-E from pregnenolone 16 alpha-carbonitrile-treated rats using modifications of previous methods and compared its 4-hydroxylase activity with other purified rat cytochromes P-450. P-450PCN-E had the highest activity among the 10 purified rat cytochromes P-450 tested and antibodies raised to P-450PCN-E completely inhibited mephenytoin 4-hydroxylase in rat liver microsomes, suggesting the involvement of P-450PCN-E in this reaction. The microsomal concentration of P-450PCN-E, estimated by immunoelectrophoretic blotting analysis, correlated well with the hydroxylase activity in rat liver microsomes (r = 0.906). Mephenytoin induced P-450PCN-E as well as other phenobarbital-inducible cytochromes P-450.
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D065731:Cytochrome P-450 CYP2C19; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004790:Enzyme Induction; D005037:Ethylmorphine-N-Demethylase / Q000378:metabolism; D006827:Hydantoins / Q000378:metabolism*; D006900:Hydroxylation; D007527:Isoenzymes / Q000378:metabolism; D008617:Mephenytoin / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D011285:Pregnenolone Carbonitrile / Q000494:pharmacology*; D051381:Rats
chemical_list: D006827:Hydantoins; D007527:Isoenzymes; D011285:Pregnenolone Carbonitrile; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D005037:Ethylmorphine-N-Demethylase; D008617:Mephenytoin