Studies on the hormone action at the target tissues: Activation of receptor and metabolism of DNA

从大鼠肾脏中纯化了胞质3,5,3′-三碘- 1 -甲状腺原氨酸（T_3）结合蛋白（CTBP）。通过凝胶排斥实验、蔗糖密度梯度离心和sds -聚丙烯酰胺凝胶电泳对CTBP的分子量进行了估算，结果表明CTBP的MR值为58000，与核T_3受体的MR值不同。纯化的CTBP被NADPH或NADP在-SH残基存在下激活。计算了CTBP的最大结合能力，得到了一个CTBP分子可以结合一个T_3分子。T_3与CTBP的结合亲和性与核T_3受体相同，但核T_3受体的分子大小不同。这些吡啶核苷酸在不改变亲和常数的情况下增加了最大结合能力。nadph激活的CTBP不与细胞核结合。然而，nadp激活的CTBP可以与细胞核结合。用0.5 M NaCl萃取，分离得到nadp活化CTBP的受体蛋白。受体蛋白分子量为20万。因此，nadph激活的CTBP可能作为细胞内T_3的储存库发挥作用。nadph激活的CTBP可能在细胞核内T_3与其特异性受体结合诱导的基因表达调控中发挥作用。NADP和NADPH是t3诱导基因表达的反调控因子。

Cytosolic 3,5,3'-triiodo-l-thyronine(T_3)-binding protein(CTBP) was purified from rat kidney. The molecular weight of CTBP was estimated by gel exclusion study, sucrose density gradient centrifugation and SDS-polyacrylamide gel electrophoresis, and gave a result that MR was 58,000,which was different from that of nuclear T_3 receptor. The purified CTBP was activated by NADPH or by NADP in the presence of -SH residue. The maximal binding capacity was calculated and gave a result that one molecule of CTBP can bind one molecule of T_3. The affinity of T_3 binding to CTBP was identical to that of nuclear T_3 receptor, although nuclear T_3 receptor had a different molecular size.These pyridine nucleotides increased the maximal binding capacity without changes in the affinity constant. NADPH-activated CTBP did not bind to nuclei. However, the NADP-activated CTBP could bind to the nuclei. By extraction with 0.5 M NaCl, acceptor protein for NADP-activated CTBP was isolated. The molecular weight of the acceptor protein was 200,000. NADPH-activated CTBP, therefore, may play a role as a reservoir for intracellular T_3. And NADPH-activated CTBP may play a role in the regulation of gene expression induced by T_3 binding to its specific receptor in nuclei. NADP and NADPH take play as counterregulatory factors for T_3-induced gene expression.