Characterization of a zebrafish estrogen-sulfating cytosolic sulfotransferase: inhibitory effects and mechanism of action of phytoestrogens.
Cytosolic sulfotransferases (STs) are generally thought to be involved in detoxification of xenobiotics, as well as homeostasis of endogenous compounds such as thyroid/steroid hormones and catecholamine hormones/neurotransmitters. We report here the identification and characterization of a zebrafish estrogen-sulfating cytosolic ST. The zebrafish ST was bacterially expressed, purified, and examined for enzymatic activities using a variety of endogenous compounds as substrates. Results showed that the enzyme displayed much higher activities toward two endogenous estrogens, estrone (E(1)) and 17beta-estradiol (E(2)), in comparison with thyroid hormones, 3,3',5-triiodothyronine (T(3)) and thyroxine (T(4)), dopamine, dihydroxyphenylalanine (Dopa), and dehydroepiandrosterone (DHEA). The kinetic parameters, K(m), and V(max), with estrogens and thyroid hormones as substrates were determined. The calculated V(max)/K(m) for E(1), E(2), T(3), and T(4) were, respectively, 31.6, 16.7, 1.5, and 0.8 nmol min(-1) mg(-1) microM(-1), indicating clearly the estrogens being preferred physiological substrates for the enzyme. The inhibitory effects of isoflavone phytoestrogens on the sulfation of E(2) by this zebrafish ST were examined. The IC(50) determined for quercetin, genistein, and daidzein were 0.7, 2.5, and 8 microM, respectively. Kinetic analyses revealed that the mechanism underlying the inhibition by these isoflavones to be of the competitive type.
Ohkimoto
Kei
K
Biomedical Research Center, The University of Texas Health Center, 11937 US Highway 271, Tyler, TX 75708, USA.
Liu
Ming Yih
MY
Suiko
Masahito
M
Sakakibara
Yoichi
Y
Liu
Ming-Cheh
MC
D000818:Animals; D003600:Cytosol / Q000201:enzymology* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004967:Estrogens / Q000378:metabolism*; D019833:Genistein / Q000378:metabolism / Q000494:pharmacology; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D007529:Isoflavones / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D048789:Phytoestrogens; D028321:Plant Preparations / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D011794:Quercetin / Q000378:metabolism / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013379:Substrate Specificity; D015238:Sulfotransferases / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013963:Thyroid Hormones / Q000378:metabolism; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
D004967:Estrogens; D007529:Isoflavones; D048789:Phytoestrogens; D028321:Plant Preparations; D011993:Recombinant Fusion Proteins; D013963:Thyroid Hormones; D029961:Zebrafish Proteins; C004742:daidzein; D011794:Quercetin; D019833:Genistein; D005982:Glutathione Transferase; D015238:Sulfotransferases