Inhibition of 17,20(17-hydroxyprogesterone)-lyase by progesterone |
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Authors: | Damodar K Mahajan Leo T Samuels |
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Institution: | Department of Biochemistry, University of Utah College of Medicine and the Eleanor Roosevelt Cancer Foundation Research Institute Salt Lake City, Utah 84132, USA |
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Abstract: | 14C-17-Hydroxyprogesterone was incubated with 7000 × g × 20 min supernatants of rat testis homogenates in the presence of various concentrations of 3H-progesterone, both under conditions where metabolism would take place and where it would be prevented. When metabolism was prevented, the ratio of progesterone to 17-hydroxyprogesterone in the microsomal fraction was 3 times that which was added to the incubation medium.Progesterone competitively inhibited 17,20-lyase action on added 17-hydroxyprogesterone but not on 17-hydroxyprogesterone formed from the added progesterone. The rate of formation of 17-hydroxyprogesterone from progesterone, however, was inhibited by added 17-hydroxyprogesterone. The results indicate that there is no free exchange of an intermediate between progesterone and androstenedione with the soluble fraction, either inside or outside the microsomal vesicle. The limited exchange with 17-hydroxyprogesterone in solution probably represents exchange with an enzyme-bound intermediate. |
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