title: Partial characterization of the cytoplasmic 20 alpha-hydroxysteroid dehydrogenase (EC 1.1.1.149) of the human placenta at term.
abstract: The 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSDH) is a key enzyme in human fetal and maternal progesterone metabolism. In this paper, the cytoplasmic 20 alpha-HSDH of human term placenta is partially characterized in vitro. A 14-fold concentration of the 20 alpha-HSDH was prepared by ultracentrifugation and ammonium sulfate precipitation. The apparent Km values for the substrates progesterone (Km: 4.8 x 10(-5) M) and 20 alpha-DHP (Km: 6.2 x 10(-5) M) and for the cofactors NADPH (Km: 1.9 x 10(-4)) and NADH (Km: 2.6 x 10(-4)) were determined. The temperature optimum for the oxidation of 20 alpha-DHP is 40--50 degrees C. The pH optimum for the reduction of progesterone was found to be pH 6.2 and for the oxidation of 20 alpha-DHP pH 6.5. The addition of glycerol (3 M) to the incubation medium inhibited the conversion rate of 20 alpha-HSDH by 70%. No influence of EDTA could be found. Various bivalent metal ions (1--100 mM) showed a dose-dependent inhibition of 20 alpha-HSDH; a complete inhibition was achieved at 100 mM: Cu2+, Zn2+, Cd2+, Fe2+ and Ni2+.
mesh_terms: D015089:20-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004092:20-alpha-Dihydroprogesterone / Q000378:metabolism; D043607:20-alpha-Hydroxysteroid Dehydrogenase; D002413:Cations, Divalent; D003593:Cytoplasm / Q000201:enzymology; D005260:Female; D006801:Humans; D007700:Kinetics; D009243:NAD / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011374:Progesterone / Q000378:metabolism
chemical_list: D002413:Cations, Divalent; D009243:NAD; D004092:20-alpha-Dihydroprogesterone; D011374:Progesterone; D009249:NADP; D015089:20-Hydroxysteroid Dehydrogenases; D043607:20-alpha-Hydroxysteroid Dehydrogenase