title: Unique induction of cytochrome P-450 isozymes in rat liver microsomes by treatment with 3,4,5,3',4'-pentachlorobiphenyl and its effect on testosterone metabolism.
abstract: Pretreatment of male Wistar rats with 3,4,5,3',4'-pentachlorobiphenyl (PenCB), a potent 3-methylcholanthrene-type inducer, increased selectively 7 alpha-but strongly repressed 2 alpha-, 6 beta- and 16 alpha-hydroxylations of testosterone in the liver microsomes. To understand this unique phenomenon, the testosterone metabolism by three isozymes (P-452, P-448 L and P-448 H) of cytochrome P-450 purified from Wistar rats treated with PenCB was studied in a reconstituted system. For comparison 4 other isozymes (P-451 I, P-451 II, P-450 II and P-450 III) of cytochrome P-450 from untreated and phenobarbital-treated rats were also studied. In addition, the contribution of cytochrome P-450's to testosterone hydroxylation was examined by an immune complex inhibition of the activity and by a determination of the individual cytochrome P-450 in microsomes using antibodies. In the reconstituted system, 7 alpha-hydroxylation of testosterone was catalyzed almost exclusively by P-452, with the exception of P-451 I. On the other hand, the 6 beta-hydroxylation was catalyzed by most of the cytochrome P-450's tested at considerably lower rates. Among the seven forms, P-451 II was the most effective catalyst for 2 alpha- and 16 alpha-hydroxylations, with equally high turnover numbers, while other forms showed only low or no activity for either or both hydroxylations. The microsomal activity of 7 alpha-hydroxylation in PenCB-treated rats was inhibited almost completely by anti-P-452. A partial inhibition of the 16 alpha-hydroxylation was achieved by anti-P-451 II and anti-P-452 while the 6 beta-hydroxylation was insensitive to anti-P-451 II but slightly sensitive to anti-P-452. The activity of 2 alpha-hydroxylation was not detected in the liver microsomes from PenCB-treated rats. Immunochemical quantitation showed that in the microsomes from PenCB-treated rats, P-451 II, P-452, P-448 L and P-448 H accounted for 4.1, 3.6, 31.6 and 62.8%, respectively, of the total cytochrome P-450 (2.69 nmol/mg protein). On the other hand, the microsomal cytochrome P-450 in untreated rat livers (0.83 nmol/mg protein) consisted of 62.7% as P-451 II, less than 1% as P-452 and the remainder as P-451 I and other unknown forms.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000818:Animals; D000906:Antibodies / Q000502:physiology; D000936:Antigen-Antibody Complex / Q000502:physiology; D001189:Aryl Hydrocarbon Hydroxylases; D002384:Catalysis; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000276:immunology; D000072467:Cytochrome P450 Family 2; D004790:Enzyme Induction; D006900:Hydroxylation; D005779:Immunodiffusion; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000096:biosynthesis*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology* / Q000378:metabolism; D011078:Polychlorinated Biphenyls / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D039181:Steroid 16-alpha-Hydroxylase; D013739:Testosterone / Q000378:metabolism*
chemical_list: D000906:Antibodies; D000936:Antigen-Antibody Complex; D007527:Isoenzymes; D013739:Testosterone; D003577:Cytochrome P-450 Enzyme System; D011078:Polychlorinated Biphenyls; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; C023035:3,4,5,3',4'-pentachlorobiphenyl