PARTICIPATION OF CYTOCHROME-P-450 IN REDUCTIVE METABOLISM OF 1-NITROPYRENE BY RAT-LIVER MICROSOMES

  • 1 January 1984
    • journal article
    • research article
    • Vol. 44  (8) , 3169-3173
Abstract
Reductive metabolism of carcinogenic 1-nitropyrene by rat liver microsomes and reconstituted cytochrome P-450 systems was investigated. Under the N atmosphere, 1-aminopyrene was the only detected metabolite of 1-nitropyrene. The reductase activity in liver 105,000 .times. 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 O2, CO, 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 4 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 indicate the central role of cytochrome P-450 in the reductive metabolism of 1-nitropyrene in liver microsomes.