This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hara, E. Articles by Tagashira, Y. Search for Related Content PubMed PubMed Citation Articles by Hara, E. Articles by Tagashira, Y.

Immunochemical Study on the Contributions of Two Molecular Species of Microsomal Cytochrome P-450 to the Metabolism of Benzo(a)pyrene by Rat Liver Microsomes¹

Department of Biochemistry, Saitama Cancer Research Institute, Ina-machi, Kitaadachi-gun, Saitama 362, Japan

The roles of two species of cytochrome P-450, the major cytochrome P-450 components of liver microsomes of phenobarbital-treated rats (PB-P-450) and 3-methylcholanthrenetreated rats (MC-P-448), were studied in the metabolism of benzo(a)pyrene in rat liver microsomes in vitro.

Benzo(a)pyrene was incubated with polychlorinated biphenyltreated rat liver microsomes, in which PB-P-450 and MC-P-448 constituted about 45 and 24% of the total cytochrome P-450, respectively. Then the metabolites were separated into those soluble in ethyl acetate and in water, and those covalently bound to protein. Using high-pressure liquid chromatography, the ethyl acetate-soluble metabolites were separated into three major groups, phenols, quinones, and dihydrodiols, including peaks of three unknown materials.

Addition of anti-MC-P-448 immunoglobulin to the reaction mixture completely inhibited the formation of all ethyl acetatesoluble metabolites. In contrast, anti-PB-P-450 immunoglobulin did not inhibit the formations of 4,5-dihydro-4,5-dihydroxybenzo(a)pyrene and 3-hydroxybenzo(a)pyrene; partially inhibited the formations of 7,8-dihydro-7,8-dihydroxybenzo(a)pyrene, 9,10-dihydro-9,10-dihydroxybenzo(a)pyrene, and the three unknown materials; and caused 30 to 40% enhancement of the formations of 9-hydroxy-benzo(a)pyrene and benzo(a)pyrene-3,6-dione and 80% enhancement of that of benzo(a)pyrene-1,6-dione. Antibody against MC-P-448, but not against PB-P-450, also caused 75% inhibition of the formation of water-soluble metabolites and 85% inhibition of formation of benzo(a)pyrene metabolites covalently bound to protein.

These results show that MC-P-448 is important in the metabolism of benzo(a)pyrene.

¹ This work was partly supported by a Grant-in-Aid for Cancer Research from the Ministry of Education, Science and Culture.

² To whom requests for reprints should be addressed.

Received 11/ 3/82. Accepted 5/ 5/83.