In Vitro Conversion of Estradiol-17β into Estrone in Normal Human Myometrium und Leiomyoma

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Abstract
The specific activity of 17.beta.-hydroxysteroid dehydrogenase was measured in normal human myometrium, and in leiomyoma specimens obtained from the same tumor-bearing uterus. In all cases the normal tissue showed greater conversion of estradiol-17.beta. into estrone than the neoplastic tissues. In normal myometrium of fertile women, the specific enzyme activity depended on the phase of the menstrual cycle, the highest values of 17.beta.-hydroxysteroid dehydrogenase activity being found in the early secretory phase. To determine the intracellular distribution of the 17.beta.-hydroxysteroid dehydrogenase, purified microsomes, mitochondria, nuclei and cytosol fractions were prepared. The purity of each fraction was monitored by marker enzymes. The enzyme was located in mitochondria and microsomes. The microsomal enzyme was bound tightly to the membranes of the endoplasmic reticulum, while mitochondrial 17.beta.-hydroxysteroid dehydrogenase was associated with the outer membranes of the organelle. Kinetic parameters (Km-values, coenzyme requirements, temperature and pH-optima) of the cytoplasmic, nuclear mitochondrial and microsomal enzyme of normal and neoplastic tissue were compared.