Kester M H, Kaptein E, Roest T J, van Dijk C H, Tibboel D, Meinl W, Glatt H, Coughtrie M W, Visser T J
Department of Internal Medicine III, Erasmus University Medical School, and Sophia Children Hospital, Rotterdam, The Netherlands.
J Clin Endocrinol Metab. 1999 Apr;84(4):1357-64. doi: 10.1210/jcem.84.4.5590.
Sulfation is an important pathway of thyroid hormone metabolism that facilitates the degradation of the hormone by the type I iodothyronine deiodinase, but little is known about which human sulfotransferase isoenzymes are involved. We have investigated the sulfation of the prohormone T4, the active hormone T3, and the metabolites rT3 and 3,3'-diiodothyronine (3,3'-T2) by human liver and kidney cytosol as well as by recombinant human SULT1A1 and SULT1A3, previously known as phenol-preferring and monoamine-preferring phenol sulfotransferase, respectively. In all cases, the substrate preference was 3,3'-T2 >> rT3 > T3 > T4. The apparent Km values of 3,3'-T2 and T3 [at 50 micromol/L 3'-phosphoadenosine-5'-phosphosulfate (PAPS)] were 1.02 and 54.9 micromol/L for liver cytosol, 0.64 and 27.8 micromol/L for kidney cytosol, 0.14 and 29.1 micromol/L for SULT1A1, and 33 and 112 micromol/L for SULT1A3, respectively. The apparent Km of PAPS (at 0.1 micromol/L 3,3'-T2) was 6.0 micromol/L for liver cytosol, 9.0 micromol/L for kidney cytosol, 0.65 micromol/L for SULT1A1, and 2.7 micromol/L for SULT1A3. The sulfation of 3,3'-T2 was inhibited by the other iodothyronines in a concentration-dependent manner. The inhibition profiles of the 3,3'-T2 sulfotransferase activities of liver and kidney cytosol obtained by addition of 10 micromol/L of the various analogs were better correlated with the inhibition profile of SULT1A1 than with that of SULT1A3. These results indicate similar substrate specificities for iodothyronine sulfation by native human liver and kidney sulfotransferases and recombinant SULT1A1 and SULT1A3. Of the latter, SULT1A1 clearly shows the highest affinity for both iodothyronines and PAPS, but it remains to be established whether it is the prominent isoenzyme for sulfation of thyroid hormone in human liver and kidney.
硫酸化是甲状腺激素代谢的一条重要途径，它通过I型碘甲状腺原氨酸脱碘酶促进激素的降解，但对于参与其中的人类硫酸转移酶同工酶却知之甚少。我们研究了人肝脏和肾脏胞质溶胶以及重组人SULT1A1和SULT1A3（分别为之前所知的偏爱苯酚和偏爱单胺的苯酚硫酸转移酶）对激素原T4、活性激素T3以及代谢物反式T3和3,3'-二碘甲状腺原氨酸（3,3'-T2）的硫酸化作用。在所有情况下，底物偏好顺序为3,3'-T2 >> 反式T3 > T3 > T4。对于3,3'-T2和T3（在50微摩尔/升3'-磷酸腺苷-5'-磷酸硫酸酯（PAPS）存在下），肝脏胞质溶胶的表观Km值分别为1.02和54.9微摩尔/升，肾脏胞质溶胶的表观Km值分别为0.64和27.8微摩尔/升，SULT1A1的表观Km值分别为0.14和29.1微摩尔/升，SULT1A3的表观Km值分别为33和1一百一十二微摩尔/升。PAPS的表观Km值（在0.1微摩尔/升3,3'-T2存在下），肝脏胞质溶胶为6.0微摩尔/升，肾脏胞质溶胶为9.0微摩尔/升，SULT1A1为0.65微摩尔/升，SULT1A3为2.7微摩尔/升。3,3'-T2的硫酸化受到其他碘甲状腺原氨酸的浓度依赖性抑制。通过添加10微摩尔/升各种类似物所获得的肝脏和肾脏胞质溶胶的3,3'-T2硫酸转移酶活性的抑制曲线，与SULT1A1的抑制曲线比与SULT1A3的抑制曲线相关性更好。这些结果表明，天然人肝脏和肾脏硫酸转移酶以及重组SULT1A1和SULT1A3对碘甲状腺原氨酸硫酸化具有相似的底物特异性。在后者中，SULT1A1对碘甲状腺原氨酸和PAPS均表现出明显最高的亲和力，但它是否是人类肝脏和肾脏中甲状腺激素硫酸化的主要同工酶仍有待确定。
