Hurd R E, Santini F, Lee B, Naim P, Chopra I J
Department of Medicine, University of California Center for the Health Sciences, Los Angeles 90024-1682.
Endocrinology. 1993 Nov;133(5):1951-5. doi: 10.1210/endo.133.5.8404641.
We have employed a new in vitro assay for study of the T3 sulfation activity in rat tissues. The assay measures by RIA the generation of T3 sulfate (T3S) during incubation of T3 with cytosol of rat tissues as the source of phenol sulfotransferase(s) and 3-phosphoadenosine-5'-phosphosulfate as the sulfate donor. The conversion of T3 to T3S proceeded rapidly for 30 min at 37 C, and the optimal pH of the reaction was 8.0. Heating the cytosol at 44 C for 15 min decreased T3S production to 63% of its value at 37 C. T3 sulfation activity was plentiful in rat liver, brain, and kidney, but little activity was demonstrable in other tissues. The Km and maximum velocity of the hepatic conversion of T3 to T3S were 114 microM and 159 pmol/mg protein.h, respectively. There was a marked inhibition of the conversion of T3 to T3S with salicylamide, 3'-monoiodothyronine, thyronine, and rT3; the IC50 of these inhibitors approximated 15, less than 0.1, 9.5, and 43 microM, respectively. On day 17 of gestation, the T3 to T3S conversion activity was more abundant in fetal skin than in other fetal tissues. However, the activity decreased in fetal skin while it increased in fetal liver, kidney, and brain nearer to term on day 20. Placenta demonstrated lower T3 to T3S conversion activity than several fetal or maternal tissues. There was no effect of hypothyroidism or hyperthyroidism on T3 sulfation activity. We conclude that T3 sulfation activity in the rat is 1) most abundant in liver, kidney, and brain tissues of the adult; 2) inhibited more avidly by 3'-monoiodothyronine than other thyronines; 3) very abundant in fetal skin early in gestation; and 4) little affected by the thyroidal status of the animal.
我们采用了一种新的体外试验来研究大鼠组织中的T3硫酸化活性。该试验通过放射免疫分析法（RIA）测定在T3与大鼠组织胞浆（作为酚磺基转移酶的来源）以及3-磷酸腺苷-5'-磷酸硫酸酯（作为硫酸供体）孵育期间T3硫酸盐（T3S）的生成。在37℃下，T3向T3S的转化在30分钟内迅速进行，反应的最佳pH值为8.0。将胞浆在44℃加热15分钟可使T3S生成量降至其在37℃时的63%。T3硫酸化活性在大鼠肝脏、脑和肾脏中丰富，但在其他组织中几乎检测不到活性。肝脏中T3向T3S转化的Km值和最大速度分别为114微摩尔和159皮摩尔/毫克蛋白·小时。水杨酰胺、3'-单碘甲状腺原氨酸、甲状腺素和反T3对T3向T3S的转化有明显抑制作用；这些抑制剂的IC50分别约为15、小于0.1、9.5和43微摩尔。在妊娠第17天，胎儿皮肤中T3向T3S的转化活性比其他胎儿组织更丰富。然而，在妊娠第20天接近足月时，胎儿皮肤中的活性下降，而胎儿肝脏、肾脏和脑中的活性增加。胎盘显示出比几种胎儿或母体组织更低的T3向T3S转化活性。甲状腺功能减退或亢进对T3硫酸化活性没有影响。我们得出结论，大鼠中的T3硫酸化活性：1）在成年大鼠的肝脏、肾脏和脑组织中最丰富；2）被3'-单碘甲状腺原氨酸比其他甲状腺素更强烈地抑制；3）在妊娠早期胎儿皮肤中非常丰富；4）几乎不受动物甲状腺状态的影响。
