title: Kinetic study of HCG induced decrease of microsomal 7 alpha-hydroxylase activity in rat testes.
abstract: Microsomes from rat testes were incubated with varying concentrations of 14C labelled testosterone and androstenedione. The production of 7 alpha-hydroxytestosterone and 7 alpha-hydroxyandrostenedione was followed; Km and Vm values were calculated from Lineweaver-Burk curves. A sustained treatment of rats with HCG resulted in a considerable decrease of the maximal 7 alpha-hydroxylation rats (Vm) whereas the Km value was not changed. Vm of microsomes from normal rats, when incubated with microsomes from HCG-treated animals, was also decreased substantially. It is concluded that HCG-induced depression of 7 alpha-hydroxylation capacity of testicular microsomes is at least in part due to non-competitive inhibition of the enzyme.
mesh_terms: D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013737:Testis / Q000201:enzymology*; D013739:Testosterone / Q000378:metabolism
chemical_list: D006063:Chorionic Gonadotropin; D013739:Testosterone; D000735:Androstenedione; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C029009:steroid hormone 7-alpha-hydroxylase