Comparison of estrogen sulfotransferase and pregnenolone sulfotransferase of guinea pig

Structural similarity and diversity of sulfotransferases

In the present study, four new forms of aryl sulfotransferase cDNAs have been isolated and their structures determined. A compilation of primary structures of 16 different sulfotransferases, including enzymes metabolizing endogenous chemicals and xenobiotics, showed a considerable extent of similarity among bacterial, plant and mammalian species, and indicates that these enzymes constitute a supergene family. Aryl sulfotransferase and estrogen sulfotransferase are shown to belong to a single gene family (ST1) which consists of at least four subfamilies, whereas, based on the sequence similarity, hydroxysteroid sulfotransferases constitute a distinct family (ST2). Little or no clear similarity was observed between the primary structures of enzymes N-sulfating aminosugars and those sulfating hydrophobic chemicals such as phenols, alcohols or amines, indicating that both types of enzymes diverged early in their evolutionary history. Two regions in the C-terminal parts are, however, conserved among all enzymes examined, which suggests a possibly essential role of these sites for the binding of a PAPS cofactor or for sulfate transfer.

Nuclear receptors for progesterone and estradiol in the guinea pig uterine compartment during gestation

Because progesterone suppresses myometrial contractility, the assumption is often made that the withdrawal of this steroid is a prerequisite for parturition. However, steroid patterns in maternal blood of the guinea pig do not consistently change with impending parturition and it has been claimed that progesterone does not suppress guinea pig myometrial contraction. The present study investigated progesterone and estrogen nuclear receptor binding in myometrium, endometrium, and chorion between 32 days of gestation and delivery at 67-71 days. Binding characteristics and behavior during sedimentation in sucrose density gradients were typical of the steroid hormone receptor family. Decreased progestin binding occurred in the myometrium, from a high of 1600 fmol/mg DNA at 49-51 days to a low of 450 fmol/mg DNA (P < 0.01) on the day of detectable pubic relaxation. This decrease commenced at 60-63 days just before the onset of relaxation. A similar, though less well defined change occurred in endometrium. Estradiol nuclear receptor binding in myometrium remained at about 350 fmol/mg DNA from 32 days until 1-2 days pre-partum when it increased to about 650 fmol/mg DNA (P < 0.05). Estradiol binding in endometrium showed an inconsistent pattern and chorion binding for both progestin and estradiol was low and unremarkable. We conclude that there is a potential for decreased progesterone effect in myometrium at about one week before delivery and increased estrogen action in that tissue immediately before delivery.

Transformation of estrone, estradiol, and estrone sulfate in uterine and vaginal isolated cells of fetal guinea pig. Effect of various antiestrogens in the conversion of estrone sulfate to estradiol

The metabolism of physiological concentrations (5 x 10(-9) M) of [3H]estrone (E1), [3H]estradiol (E2), and [3H]estrone sulfate (E1S) was studied in isolated fetal uterine and vaginal cells of guinea pigs in culture. After 24 hours of incubation in both cells, a large percentage (40-60%) of E1 is converted to E2; however, after incubation of E2, most of the radioactive material (45-65%) corresponds to unchanged E2. Similarly, in the incubation medium the concentration of E2 is significantly higher related to E1 after incubation with E1 or E2. An intense sulfotransferase activity is found for both estrogens, whereas in the culture medium the respective sulfates represent 27-45% of the total radioactive material after incubation with the uterine cells and 15-24% for the vaginal cells. Using E1S, significant hydrolysis is observed in both cells and the analysis of the freed radioactive material indicated a high percentage in E2 (66% in the uterine cells and 71% in the vaginal cells). The conversion of E1S to E2 was strongly decreased by the antiestrogens: tamoxifen, 4-hydroxy-tamoxifen, and ICI 164,384. The inhibitory effect in relation to the incubation with E1S only was 43-66% in the uterine cells and 50-85% in the vaginal cells. The present data suggest that estrogen sulfates can play an important biological role in the target tissues of the fetus, and that the enzymatic mechanisms of the bioavailability of E2 for the biological responses of the hormone can be operated in the target tissue itself.