title: Binding of metyrapone to dithionite-reduced cytochrome P-450 from rats treated with xenobiotics.
abstract: The in vitro binding of metyrapone to dithionite-reduced cytochrome P-450 in hepatic microsomes from rats treated in vivo with thirteen different xenobiotics was studied spectrophotometrically. The proportion of cytochrome P-450 that bound metyrapone increased 1.8-fold to about 78% following treatment with phenobarbitone (PB) and PB-type inducers (trans-stilbene oxide, 2,2',4,4'-tetrachloro-, 2,2',4,5,5'-pentabromo- and 2,2',4,4',5,5'-hexachlorobiphenyl) but remained unaltered following treatment with 3-methylcholanthrene (MC) and MC-type induces (benzo[a]pyrene, beta-naphthoflavone and 3,3',4,4'-tetrabromobiphenyl). The simultaneous induction of the PB-inducible and MC-inducible forms of cytochrome P-450 by administering Aroclor 1254 or by coadministering PB with MC increased the proportion of cytochrome P-450 that bound metyrapone to 74 and 78% respectively. PB treatment increased whereas MC treatment decrease the binding affinity for metyrapone by approximately 20-fold. Treatment with isosafrole or metyrapone itself failed to stimulate metyrapone binding. In contrast, pregnenolone-16 alpha-carbonitrile was indistinguishable from PB in its ability to increase the binding capacity and binding affinity for metyrapone. Our results indicate that metyrapone binding is not specific for cytochrome P-450b, the major PB-inducible hemoprotein, as has been proposed [V. Luu-The, J. Cumps and P. Dumont, Biochem. biophys. Res. Commun. 93, 776 (1980)].
mesh_terms: D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism; D004227:Dithionite; D004790:Enzyme Induction; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008797:Metyrapone / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology*; D010084:Oxidation-Reduction; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001713:Biphenyl Compounds; D003580:Cytochromes; D004227:Dithionite; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital; D008797:Metyrapone