Studies on the involvement of lysosomes in estrogen action, III. The dehydrogenation of estradiol to estrone by porcine endometrial lysosomes.

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.