Nishiyama Takahito, Ogura Kenichiro, Nakano Hiroaki, Kaku Teppei, Takahashi Eriko, Ohkubo Yasunari, Sekine Koji, Hiratsuka Akira, Kadota Shigetoshi, Watabe Tadashi
Department of Drug Metabolism and Molecular Toxicology, School of Pharmacy, Tokyo University of Pharmacy and Life Science, Japan.
Drug Metab Pharmacokinet. 2002;17(3):221-8. doi: 10.2133/dmpk.17.221.
It is known that in humans taking soy food, the phytoestrogens, daidzein (DZ) and genistein (GS), exist as sulfates and glucuronides in the plasma and are excreted as conjugates in urine. To investigate which human sulfotransferase (SULT) isoforms participate in the sulfation of these phytoestrogens, the four major cytosolic SULTs, SULT1A1, SULT1A3, SULT1E1, and SULT2A1, occurring in the human liver were bacterially expressed as His-tagged proteins and chromatographically purified to homogeneity in the presence of Tween 20 and glycerol as highly efficient agents for stabilizing the recombinant enzymes. All the SULTs showed sulfating activity toward both DZ and GS. However, k(cat)/K(m) values observed indicated that these phytoestrogens were sulfated predominantly by SULT1A1 and SULT1E1 with K(m) values of 0.3 and 0.7 microM for GS and 1.9 and 3.4 microM for DZ, respectively. DZ and GS strongly inhibited the sulfation of the endogenous substrate, beta-estradiol, by SULT1E1 in a non-competitive manner with K(i) values of 14 and 7 microM, respectively, suggesting that these phytoestrogens might affect tissue levels of beta-estradiol in the human. The phenolic endocrine-disrupting chemicals, bisphenol A (BPA), 4-n-nonylphenol (NP), and 4-t-octylphenol (t-OP), were used as substrates to investigate the possible participation of human SULTs in their metabolism for excretion. High k(cat)/K(m) values were observed for the sulfation of BPA by SULT1A1, NP by SULT1A1 and SULT1E1, and t-OP by SULT1E1 and SULT2A1.
已知在食用大豆食品的人体内，植物雌激素黄豆苷元（DZ）和染料木黄酮（GS）在血浆中以硫酸盐和葡萄糖醛酸苷的形式存在，并以结合物的形式随尿液排出。为了研究哪些人磺基转移酶（SULT）同工型参与这些植物雌激素的硫酸化作用，将人肝脏中存在的四种主要胞质SULT，即SULT1A1、SULT1A3、SULT1E1和SULT2A1，作为带有His标签的蛋白质进行细菌表达，并在吐温20和甘油作为稳定重组酶的高效试剂存在的情况下进行色谱纯化，直至达到均一性。所有的SULT对DZ和GS都表现出硫酸化活性。然而，观察到的k(cat)/K(m)值表明，这些植物雌激素主要由SULT1A1和SULT1E1硫酸化，GS的K(m)值分别为0.3和0.7 microM，DZ的K(m)值分别为1.9和3.4 microM。DZ和GS以非竞争性方式强烈抑制SULT1E1对内源性底物β-雌二醇的硫酸化作用，K(i)值分别为14和7 microM，这表明这些植物雌激素可能会影响人体内β-雌二醇的组织水平。酚类内分泌干扰化学物质双酚A（BPA）、4-正壬基酚（NP）和4-叔辛基酚（t-OP）被用作底物，以研究人SULTs可能参与它们的代谢排泄过程。观察到SULT1A1对BPA硫酸化、SULT1A1和SULT1E1对NP硫酸化以及SULT1E1和SULT2A1对t-OP硫酸化具有较高的k(cat)/K(m)值。
