Specific binding of polyhalogenated aromatic hydrocarbon inducers of cytochrome P-450d to the cytochrome and inhibition of its estradiol 2-hydroxylase activity.
Treatment of male Sprague-Dawley rats with 3,4,5,3',4',5'-hexabromobiphenyl (HBB) at 10 mumol/kg followed by purification of hepatic microsomal cytochrome P-450d revealed that HBB remained specifically bound to P-450d throughout purification. Binding was noncovalent since HBB was removed by extraction with dichloromethane. Although HBB induced both cytochrome P-450c and P-450d, specific immunoprecipitation of these isozymes from HBB-treated rats showed that HBB was associated only with cytochrome P-450d. Quantitation of HBB and cytochrome P-450d in microsomes from HBB-treated rats suggested a 0.9:1 ratio of HBB to cytochrome P-450d. Five other halogenated aromatic hydrocarbon inducers of cytochrome P-450d, bearing steric similarity to HBB (including 2,3,7,8-tetrachlorodibenzo-p-dioxin), were associated with cytochrome P-450d when used to induce cytochrome P-450d in rats. HBB inhibited estradiol 2-hydroxylase activity of purified cytochrome P-450d in a noncompetitive manner with an I50 of 38 nM for 50 nM P-450d whereas its noncoplanar isomer, 2,4,5,2',4',5'-hexabromobiphenyl, had an I50 over 700-fold higher. Thus certain polyhalogenated aromatic hydrocarbons, with the capacity to induce cytochrome P-450d also bind to the cytochrome when used as inducing agents and inhibit catalytic activity of the cytochrome.
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D000818:Animals; D019363:Cytochrome P-450 CYP1A1; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction; D004797:Enzyme-Linked Immunosorbent Assay; D006846:Hydrocarbons, Halogenated / Q000378:metabolism* / Q000633:toxicity; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D011075:Polybrominated Biphenyls / Q000378:metabolism / Q000633:toxicity; D011078:Polychlorinated Biphenyls / Q000378:metabolism / Q000633:toxicity; D000072317:Polychlorinated Dibenzodioxins / Q000378:metabolism / Q000633:toxicity; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors*
D006846:Hydrocarbons, Halogenated; D011075:Polybrominated Biphenyls; D000072317:Polychlorinated Dibenzodioxins; D003577:Cytochrome P-450 Enzyme System; D011078:Polychlorinated Biphenyls; D013250:Steroid Hydroxylases; D019363:Cytochrome P-450 CYP1A1; C020120:estrogen 2-hydroxylase; C032790:3,3',4,4',5,5'-hexabromobiphenyl; C027309:3,4,5,3',4',5'-hexachlorobiphenyl; C023035:3,4,5,3',4'-pentachlorobiphenyl; C028451:3,4,3',4'-tetrachlorobiphenyl