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Metabolism of Benzo(a)pyrene and (-)-trans-7,8-Dihydroxy-7,8-dihydrobenzo(a)pyrene by Rat Liver Nuclei and Microsomes

Department of Biochemistry, New Jersey Medical School, College of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103 [(J. M. P., C. S. Y.], and Chemistry Branch, National Cancer Institute, Bethesda, Maryland 20014 [S. K. Y., D. W. M., H. V. G.]

The metabolism of benzo(a)pyrene and (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene was examined by high-pressure liquid chromatography. Liver nuclei or microsomes from control, 3-methylcholanthrene-treated, or phenobarbital-treated rats were used. An improved method of separating the metabolites is described. Upon treatment with 3-methylcholanthrene, metabolism of benzo(a)pyrene was enhanced 4- and 9-fold in microsomes and nuclei, respectively. No enhancement was observed with phenobarbital treatment. The pattern of metabolites obtained with nuclei was similar to that of the corresponding microsomes, although quantitatively reduced. Nuclei and microsomes also metabolized (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene to 7,8-diol-9,10-epoxides and again the metabolic pattern was similar. Each of the nuclear samples produced less diol-epoxides than did the corresponding microsomes. Treatment with 3-methylcholanthrene caused an 8-fold increase in r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo(a)pyrene (diol-epoxide I) formation with microsomes but only a 2-fold increase with nuclei. Inducible, r-7,t-8-dihydroxy-c-9,10-oxy-7,8,9,10-tetrahydrobenzo(a)pyrene (diol-epoxide II) formation was also detected. Phenobarbital treatment did not greatly increase diol-epoxide formation. Since both the microsomes and the nuclei can produce diolepoxides, both organelles may be considered as potentially important sites of carcinogen activation.

¹ Present address. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Mass. 02139.

² To whom requests for reprints should be addressed, at Department of Biochemistry, New Jersey Medical School, Newark, N. J. 07103. Recipient of National Cancer Institute Grant CA-16788, which partially supported this work.

³ Present address: Department of Pharmacology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, Md. 20014.

Received 8/25/77. Accepted 1/27/78.