Lee J K, Gordon P R, Stall G M, Gilchrest B A, Kaplan M M
Department of Medicine, New England and Medical Center Hospital, Boston.
Metabolism. 1989 Dec;38(12):1154-61. doi: 10.1016/0026-0495(89)90151-0.
Thyroid hormone metabolism was studied in the human Caco-2 colon carcinoma cell line, which at confluence exhibits several functions of differentiated enterocytes. Cells were harvested two to 17 days after reaching confluence. Intact cells and homogenates were tested for deiodination of [125I]-labeled substrates. Small amounts of thyroxine (T4) were converted by homogenates to 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), and 1-, with no detectable production of 3,5,3'-triiodothyronine (T3) by homogenates or cells. rT3 was converted to 3,3'-T2 and 1- with an apparent Michaelis constant (Km) for rT3 of 24 nmol/L; 6-n-propyl-2-thiouracil (PTU) had a 50% inhibitory concentration of 30 nmol/L and abolished rT3 5'-deiodination at 1 mmol/L in the presence of 20 mmol/L dithiothreitol (DTT). T3 was deiodinated to 3,3'-T2 and 3'-monoiodothyronine (3'-T1) with an apparent Michaelis constant (Km) for T3 of 5.7 nmol/L; this reaction was not inhibited by 1 mmol/L PTU. Phenolic and tyrosyl ring deiodinating activities were maximal four and six days, respectively, after the cells reached confluence. Homogenates of cells grown in standard medium containing fetal calf serum had fivefold higher rT3 5'-deiodinating activity than cells grown in a serum-free defined culture medium, reflecting a fivefold difference in the apparent Vmax with no difference in the apparent Km for rT3. There was no difference in T3 5-deiodination rates in homogenates of Caco-2 cells grown in the two media until 12 days postconfluence, when cells grown in standard medium had higher activity.(ABSTRACT TRUNCATED AT 250 WORDS)
在人Caco-2结肠癌细胞系中研究了甲状腺激素代谢，该细胞系在汇合时表现出分化肠上皮细胞的多种功能。细胞在达到汇合后2至17天收获。对完整细胞和匀浆进行了[125I]标记底物的脱碘测试。匀浆将少量甲状腺素（T4）转化为3,3',5'-三碘甲状腺原氨酸（rT3）、3,3'-二碘甲状腺原氨酸（3,3'-T2）和1-，匀浆或细胞均未检测到3,5,3'-三碘甲状腺原氨酸（T3）的产生。rT3被转化为3,3'-T2和1-，rT3的表观米氏常数（Km）为24 nmol/L；6-正丙基-2-硫氧嘧啶（PTU）的50%抑制浓度为30 nmol/L，在20 mmol/L二硫苏糖醇（DTT）存在下，1 mmol/L时可消除rT3的5'-脱碘作用。T3被脱碘为3,3'-T2和3'-单碘甲状腺原氨酸（3'-T1），T3的表观米氏常数（Km）为5.7 nmol/L；该反应不受1 mmol/L PTU抑制。细胞达到汇合后，酚环和酪氨酰环脱碘活性分别在第4天和第6天达到最大值。在含胎牛血清的标准培养基中生长的细胞匀浆的rT3 5'-脱碘活性比在无血清限定培养基中生长的细胞高五倍，这反映了表观最大反应速度（Vmax）相差五倍，而rT3的表观Km无差异。在两种培养基中生长的Caco-2细胞匀浆的T3 5-脱碘率在汇合后12天之前没有差异，之后在标准培养基中生长的细胞活性更高。（摘要截短于250字）
