Further Studies of Steroidal Inhibitors of Δ5,3β-Hydroxysteroid Dehydrogenase and Δ5-Δ4,3-Ketosteroid Isomerase inPseudomonas testosteroniand in Bovine Adrenals
A study has been performed to determine the effects of various steroids on the activity of Δ6,3β-hydroxysteroid dehydrogenase and Δ5-Δ4,3-ketosteroid isomerase in partially purified extracts of Pseudomonas testosteroni, and in bovine adrenal microsomes. The steroids studied affect adrenal or genital development. Of these, 2α-cyano-4,4,17α-trimethylandrost-5-en17β-ol-3-one (cyanoketone), 2-hydroxymethylene- androstan-17β-ol-3-one (hydroxymethylene) and estradiol-17β produced stoichiometric inhibition of the bacterial and bovine dehydrogenases. In a Dixon-type plot, the inhibition of both isomerases by these steroids was competitive, while that of both dehydrogenases was noncompetitive. Dialysis of inhibited enzyme preparations for 24 hr against 1000 volumes of medium completely restored activity of all enzymes inhibited by estradiol-17β, whereas activity of all enzymes inhibited by the other 2 steroids was virtually unaffected by such a dialysis. Medroxyprogesterone, l,2α-methylene- 6-chlorpregn-4,6-dien-17α-ol-3,20-dione (cyproterone), 17β-hydroxy-4,4,17α:-trimethylandrost- 5-en-(2,3d)-isoxazole (isoxazole) produced competitive inhibition of both bacterial enzymes, and the isoxazole also inhibited both bovine enzymes competitively. A similar dialysis nearly reversed the inhibition of enzymatic activity produced by medroxyprogesterone and cyproterone, but did not affect the inhibition produced by the isoxazole. These results provide further evidence to support the hypothesis that the observed effects of these steroids in mammalian development may be due in part to their tight binding to the active sites of the dehydrogenase and isomerase.