Kinetic study of HCG induced decrease of microsomal 7 alpha-hydroxylase activity in rat testes

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.