Assignment of estradiol-17β dehydrogenase and of estrone reductase to cytoplasmic structures of porcine endometrium cells

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Abstract
Homogenates of porcine endometrium contain substantial activity for the dehydrogenation of estradiol-17.beta. but little for estrone reduction. Both activities are associated with cytoplasmic structures. The dehydrogenase is characterized by a pH 7.7 optimum, Km 2.2 .times. 10-7 mol/l for estradiol and Km 4.4 .times. 10-5 mol/l for the cosubstrate NAD+. The corresponding figures for the reductase are pH 6.6, Km 1.1 .times. 10-6 mol/l for estrone and Km 2.1 .times. 10-5 mol/l for the cosubstrate NADPH. The (mitochondrial/lysosomal) 17,000 .times. g particulate fraction contains a 52-fold higher dehydrogenase than reductase activity. The (microsomal) 200,000 .times. g particulate fraction is only 16-fold richer in dehydrogenase. Isopycnic centrifugations of the two fractions in Percoll gradients reveal that estrone reductase and the coequilibrating marker enzyme cytochrome c reductase occur in constant proportions, whereas the dehydrogenase/cytochrome c reductase ratios are different. Both, the kinetic data and the structural assignments speak in favour of individual enzymes catalyzing the dehydrogenation of estradiol and the reduction of estrone. All gradient fractions exhibiting dehydrogenase activity feature small, electrondense vesicles of 0.15-0.20 .mu.m in diameter as a common structural element which might harbour the dehydrogenase.