title: Selective reactivation of steroid hydroxylases following dissociation of the isosafrole metabolite complex with rat hepatic cytochrome P-450.
abstract: In order to elucidate the isozyme specificity of complex formation between cytochrome P-450 and the isosafrole metabolite the effect of complex dissociation on different steroid hydroxylation pathways was studied in hepatic microsomal fractions. Isosafrole induction was found to increase the 16 beta- and 7 alpha-hydroxylation of androst-4-ene-3,17-dione approximately 2.8- and 1.7-fold, respectively, whereas the 16 alpha-hydroxylation pathway was decreased to about one-quarter of control activity; 6 beta-hydroxylation was unchanged from control activity. More striking changes were apparent following dissociation of the isosafrole metabolite from its complex with ferricytochrome P-450 by the steroid substrate. Thus an approximate fourfold elevation of 16 beta-hydroxylase activity was observed after displacement and 6 beta-hydroxylation increased about twofold; 7 alpha-hydroxylase activity was decreased to 0.75-fold of undisplaced activity and 16 alpha-hydroxylase activity was unchanged. These data provide convincing evidence that at least two forms of phenobarbital-inducible cytochrome P-450 (cytochromes P-450PB-B and P-450PB/PCN-E) are present to some extent in a catalytically inactive complexed state in isosafrole-induced rat hepatic microsomes. Furthermore, there is now evidence to suggest that the constitutive isozymes cytochrome P-450UT-A and cytochrome P-450UT-F are not complexed to any degree in hepatic microsomes from isosafrole-induced rats.
mesh_terms: D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2; D004149:Dioxoles / Q000378:metabolism*; D004789:Enzyme Activation; D004790:Enzyme Induction / Q000187:drug effects; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010105:Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D012451:Safrole / Q000378:metabolism* / Q000494:pharmacology; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism*
chemical_list: D004149:Dioxoles; D007527:Isoenzymes; D000735:Androstenedione; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; D012451:Safrole; C015959:isosafrole