title: Examination of differences between benzo[a]pyrene and steroid hydroxylases in guinea pig adrenal microsomes.
abstract: The effects of antibodies to cytochromes P-45017 alpha,lyase and P-450C21 on benzo[a]pyrene hydroxylase activity were measured in microsomes from guinea pig adrenals. Anti-cytochrome P-45017 alpha,lyase IgG inhibited about 30% of the benzo[a]pyrene hydroxylase activity of the microsomes in the presence of excess amounts of the IgG, but anti-cytochrome P-450C21 IgG did not affect the activity. In a reconstituted system, consisting of cytochrome P-450, NADPH-cytochrome-P-450 reductase and dilauroylphosphatidylcholine, cytochrome P-45017 alpha,lyase catalyzed, in addition to steroid hydroxylation, benzo[a]pyrene hydroxylation, but cytochrome P-450C21 did not hydroxylate benzo[a]pyrene. Since anti-cytochrome P-45017 alpha,lyase IgG inhibited benzo[a]pyrene hydroxylase activity completely in the reconstituted system with cytochrome P-45017 alpha,lyase, the presence of non-inhibited benzo[a]pyrene hydroxylase in the microsomes suggests that the residual activity in the microsomes may be due to some enzyme other than cytochrome P-45017 alpha,lyase. Benzo[a]pyrene hydroxylase activity was detected in detergent-solubilized microsomes from which cytochrome P-45017 alpha,lyase was removed by using an immobilized anti-cytochrome P-45017 alpha,lyase IgG-Sepharose column. This shows the existence in microsomes of a benzo[a]pyrene hydroxylase other than cytochrome P-45017 alpha,lyase. Benzo[a]pyrene hydroxylase in the solubilized microsomes required O2, NADPH and NADPH-cytochrome-P-450 reductase for its activity and was inhibited by CO. This suggests that benzo[a]pyrene hydroxylase is a cytochrome P-450-dependent monooxygenase. This novel enzyme was also active in xenobiotic metabolism, such as 2-nitropropane denitrification and aminopyrine demethylation.
authors.affiliation: Faculty of Integrated Arts and Sciences, Hiroshima University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Mochizuki
authors.forename: S
authors.initials: S
authors.lastname: Kominami
authors.forename: S
authors.initials: S
authors.lastname: Takemori
mesh_terms: D000311:Adrenal Glands / Q000201:enzymology*; D000818:Animals; D000936:Antigen-Antibody Complex; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D001579:Benzopyrene Hydroxylase / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006168:Guinea Pigs; D007106:Immune Sera; D007074:Immunoglobulin G; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D013250:Steroid Hydroxylases / Q000378:metabolism*
chemical_list: D000936:Antigen-Antibody Complex; D007106:Immune Sera; D007074:Immunoglobulin G; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001579:Benzopyrene Hydroxylase; D001189:Aryl Hydrocarbon Hydroxylases