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. By differential centrifugation of homogenate fractions and isopycnic separation of the particles sedimenting in the 600 leads to 38000 x g range, accompanied by marker enzyme and electron microscopic analyses, the enzyme appears to be exclusively associated with a subpopulation of lysosomes. It displays a high affinity for estradiol with a Km = 5 x 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 two cosubstrates.