In vivo and in vitro study of the mechanism of action of a synthetic progestin in lowering unconjugated estradiol and total estriol in plasma during normal human pregnancy

Inhibition of human placental sterylsulfatase by synthetic analogs of estrone sulfate

Synthetic analogs of estrone sulfate which carry differently substituted sulfonyl groups at position 3 of an invariable 3-desoxyestrone (dE1) moiety were tested in vitro as inhibitors of the human placental sterylsulfatase. Using both placental microsomes and a highly purified placental sterylsulfatase preparation as the enzyme source and dehydroepiandrosterone [35S]sulfate or estrone [35S]sulfate as the substrate, the following order of inhibitory potencies was observed: dE1-3-sulfonylchloride > dE1-3-sulfonylfluoride approximately dE1-3-sulfonate > dE1-3-sulfonamide approximately 3-methylsulfonyl-dE1. According to the results, the association of enzyme and inhibitor appears to be favored by an electronegative substituent at the sulfur atom (-C1, -F, -O-). Since, however, even the most potent synthetic inhibitor was bound by the enzyme with significantly lower affinity than was the natural substrate estrone sulfate, an oxygen function between the aromatic ring and the sulfur atom may be necessary for high affinity binding towards the sterylsulfatase. In addition to its fast reversible association with the enzyme, dE1-3-sulfonylchloride further affected the sulfatase activity in a time-dependent manner. This latter inhibitory activity which may be due to a covalent modification (alkylation) of sterylsulfatase by the analog was partially prevented in the presence of substrate.