title: Participation of cytochrome P-450 in reductive metabolism of 1-nitropyrene by rat liver microsomes.
abstract: Reductive metabolism of carcinogenic 1-nitropyrene by rat liver microsomes and reconstituted cytochrome P-450 systems was investigated. Under the nitrogen atmosphere, 1-aminopyrene was the only detected metabolite of 1-nitropyrene. The reductase activity in liver 105,000 X g supernatant fraction was ascribed to DT-diaphorase, aldehyde oxidase, and other unknown enzyme(s) from the results of cofactor requirements and inhibition experiments. The microsomal reductase activity was inhibited by oxygen, carbon monoxide, 2,4-dichloro-6-phenylphenoxyethylamine, and n-octylamine. Flavin mononucleotide markedly enhanced the activity, and 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride also enhanced it, but slightly. The microsomal activity was induced by the pretreatment of rats with 3-methylcholanthrene, sodium phenobarbital, or polychlorinated biphenyl, and the increments of the activity correlated well with those of the specific contents of cytochrome P-450 in microsomes. The reductase activity could be reconstituted by NADPH-cytochrome P-450 reductase and forms of cytochrome P-450 purified from liver microsomes of polychlorinated biphenyl-induced rats. Among four forms of cytochrome P-450 examined, an isozyme P-448-IId which showed high activity in hydroxylation of benzo(a)pyrene catalyzed most efficiently the reduction of 1-nitropyrene. The results of this study indicate the central role of cytochrome P-450 in the reductive metabolism of 1-nitropyrene in liver microsomes.
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009601:Nitroreductases; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D011721:Pyrenes / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D011721:Pyrenes; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D009251:NADPH-Ferrihemoprotein Reductase; C037214:1-nitropyrene reductase; D009601:Nitroreductases; C032668:1-nitropyrene