Steroid Sulfatase Activity in Human Fetal Membranes

Abstract

The human fetal membranes appear to play an important role in transport and metabolism of steroids, in the maintenance of pregnancy and perhaps in the metabolic processes leading to the initiation of parturition. Therefore, steroid sulfatase activity of human fetal membranes was studied and found to reside in the chorion laeve, with the amnion totally devoid of this activity. Within the chorion laeve, the highest specific activity of sulfatase was found in a subcellular fraction rich in microsomes. Dehydroisoandrosterone sulfate and pregnenolone sulfate had similar affinities for the sulfatase enzyme with a Km of 6 μM and 4 μM, respectively. Using [³H]dehydroisoandrosterone sulfate as the substrate and chorion laeve microsomes, the pH optimum was 7.0 and the apparent temperature optimum was 53 C. Sulfatase activity on [³H]dehydroisoandrosterone sulfate was inhibited by a variety of steroid sulfates, and the enzymatic activity was unchanged by freezing and thawing. After incubation of minces of chorion laeve with [³H]dehydroisoandrosterone sulfate in the presence of NADPH, [³H]dehydroisoandrosterone, [³H]4-androstene-3,17-dione, [³H]testosterone and [³H]5α-androstane-3,17-dione were isolated as products, thus showing that chorion laeve has 3β-hydroxysteroid oxidoreductase-Δ^5→4-isomerase, 17β-hydroxysteroid oxidoreductase, and 5α-reductase enzyme systems.