Human Placental 17β-Estradiol Dehydrogenase

Two estrogen-sensitive pyridine nucleotide transhydrogenase systems of human placenta have been examined and shown to be separate and distinct entities by both physical and kinetic properties. The 17β-estradiol-activated transhydrogenase of human placenta has been shown to be free from 17β-estradiol dehydrogenase activity by a direct assay procedure which utilizes 17β-estradiol-6,7-3H-17α-2H. Rechromatography of the 17β-estradiol-activated transhydrogenase did not cause generation of dehydrogenase activity. Its activation does not involve oxidation-reduction at C-17 of 17β-estradiol. The 17β-estradiol-activated transhydrogenase is stimulated by 17β-estradiol-17α-2H without loss of 2H and by diethylstilbestrol, but not by estrone or by 17αmethylestra-1,3,5(10)-triene-3,17β-diol. The transhydrogenase function of 17β-estradiol dehydrogenase involves a cyclic oxidation-reduction of the C-17 alcohol, as shown by formation of estrone and loss of 2H from 17β-estradiol-17α2H. It is stimulated by 17β-estradiol and by estrone but neither by diethylstilbestrol nor by 17α-methylestra-1,3,5(10)-triene-3,17β-diol.