Sorimachi K, Niwa A, Yasumura Y
Biochim Biophys Acta. 1980 Jul 15;630(4):469-75. doi: 10.1016/0304-4165(80)90001-x.
The cultured rat hepatoma cell (R117--21B) homogenates metabolized 3,[3',5'-125I]triiodothyronine by phenolic ring deiodination and produced radioactive iodide and 3,3'-diiodothyronine. Thyroxine (T4) was converted to 3,3',5-triiodothyronine (T3). The production of 125I- represented the deiodination was observed to be pH 6.0--7.0. This enzyme reaction was accelerated by dithiothreitoil. Propylthiouracil strongly inhibited the phenolic ring deiodination at 0.1 mM, whereas an effect of 20 mM methylmercaptoimidazol on the deiodination was very weak or absent. Excess unlabeled iodothyronines (T4, T3 and 3,5-diiodo-L-thyronine) inhibited the phenolic ring deiodination of labeled 3,3',5'-triiodothyronine, although their inhibitory effect was slightly different. Triiodothyroacetic acid was a better inhibitor than T3. Diiodotyrosine did not affect phenolic ring deiodination in cultured rat hepatoma cell homogenates. Phenolic and nonphenolic ring deiodinase activities of cultured monkey hepatocarcinoma cell and rat liver homogenates were also studied by the use of 3,[3',5'-125I]triiodothyronine and [3,5-125I]thyroxine, respectively. Both deiodinase activities were observed in particulate fractions (mitochondrial and microsomal) of cultured cell and rat liver homogenates.
培养的大鼠肝癌细胞（R117--21B）匀浆通过酚环脱碘作用代谢3，[3'，5'-125I]三碘甲状腺原氨酸，产生放射性碘化物和3，3'-二碘甲状腺原氨酸。甲状腺素（T4）被转化为3，3'，5-三碘甲状腺原氨酸（T3）。观察到125I-的产生代表脱碘作用的pH值为6.0--7.0。二硫苏糖醇可加速该酶反应。丙硫氧嘧啶在0.1 mM时强烈抑制酚环脱碘作用，而20 mM甲巯咪唑对脱碘作用的影响非常微弱或不存在。过量的未标记碘甲状腺原氨酸（T4、T3和3，5-二碘-L-甲状腺原氨酸）抑制标记的3，3'，5'-三碘甲状腺原氨酸的酚环脱碘作用，尽管它们的抑制作用略有不同。三碘甲状腺乙酸是比T3更好的抑制剂。二碘酪氨酸对培养的大鼠肝癌细胞匀浆中的酚环脱碘作用没有影响。还分别使用3，[3'，5'-125I]三碘甲状腺原氨酸和[3，5-125I]甲状腺素研究了培养的猴肝癌细胞和大鼠肝脏匀浆的酚环和非酚环脱碘酶活性。在培养细胞和大鼠肝脏匀浆的颗粒部分（线粒体和微粒体）中均观察到了两种脱碘酶活性。
