Studies on the Involvement of Lysosomes in Estrogen Action, III. The Dehydrogenation of Estradiol to Estrone by Porcine Endometrial Lysosomes

Abstract

Endometrial cells from prepuberal pigs contain an estradiol 17.beta.-dehydrogenase [E.C. 1.1.1.62]. By differential centrifugation of homogenate fractions and isopycnic separation of the particles sedimenting in the 600 .fwdarw. 38,000 .times. g range, accompanied by marker enzyme and EM analyses, the enzyme appears to be exclusively associated with a subpopulation of lysosomes. It displays a high affinity for estradiol with a Km = 5 .times. 10-7 mol/l. Dehydrogenation of estradiol to estrone is favorably driven by NAD+, poorly by NADP+. The reverse reaction with estrone as substrate and either NADH or NADPH or NADPH+ regenerating system as cosubstrate does not proceed beyond the detection level, but trace amounts of 6 .alpha.-/7 .alpha.-hydroxyestrone are observed at pH 6.5 with the latter 2 cosubstrates.