17β-Hydroxysteroid dehydrogenase in monkey endometrium: Characterization of enzyme activity, and effects of estradiol alone or in combination with progesterone

Abstract

17β-Hydroxysteroid dehydrogenase (HSD) was studied in endometrium removed surgically from intact female monkeys in the luteal phase of the menstrual cycle. Also castrated monkeys ( N = 20) implanted with estradiol ( E 2) and progesterone (P) in silastic capsules were used to investigate the hormonal dependence of this enzyme in endometrium. The activity was characterized by an optimal pH between 9 and 10, a Km for E 2 of 14.2 × 10 −6M, a Vmax of 0.9 × 10 −6M × min −1 in Tris-HCl buffer 50 mM pH 9. Using these conditions, we found linearity with time and protein concentration. Subcellular fractionation of endometrial homogenate showed a maximal activity in the 105,000 × g ultracentrifugation microsomal pellet and a very low activity in cytosol. HSD activity increased slightly, but distinctly, with E 2 capsules alone, and a marked HSD stimulation (10 fold) occurred after P administration in combination with E 2. There are strong similarities between this enzyme and the one described in human endometrium.