Binding of thyroid hormones in serum and liver cytosol of Rana catesbeiana tadpoles.
Binding of thyroid hormones in serum and liver cytosol of Rana catesbeiana tadpoles.
复制标题
林蛙蝌蚪血清和肝细胞质中甲状腺激素的结合。
作者：
V. Galton
本文用平衡透析法和葡聚糖包被活性炭法研究了蝌蚪血清和肝胞液中甲状腺激素与蛋白质的结合。通过平衡透析直接测量，血清中约1%的总T3或T4和细胞溶质（1：5或1：10稀释）中不到0.5%的总T3和T4以游离形式存在。游离T3和T4组分在10（-10）和10（-6）M之间与激素浓度无关。由活性炭结合技术测定的游离激素分数的值远高于直接测定的值，并且很明显，如果任何蛋白质-激素复合物非常迅速地解离，则该技术不能用于测量游离激素分数。然而，使用木炭技术获得了重要信息。结果发现，细胞质和血清都含有许多结合甲状腺激素的位点，其中一些是饱和的。然而，可饱和位点对T4和T3的亲和力相对较低。过量激素的替代结合位点的存在防止了在高激素浓度下游离部分的任何增加。没有证据表明，在细胞质或血清中的任何高亲和力，低容量的结合位点类似于蝌蚪肝细胞核中检测到的。这表明，结合甲状腺激素在血清和肝细胞质中的蝌蚪服务的功能以外的甲状腺激素的行动的启动。
Binding of thyroid hormones to proteins in tadpole serum and liver cytosol was studied using both equilibrium dialysis and dextran-coated charcoal techniques to separate bound and free hormone. Measured directly by equilibrium dialysis, approximately 1% of the total T3 or T4 in serum and less than 0.5% of the total T3 and T4 in cytosol (diluted 1:5 or 1:10) were in the free form. Free T3 and T4 fractions were independent of hormone concentration between 10(-10) and 10(-6) M. Values for free hormone fractions determined by the charcoal-binding technique were much higher than those determined directly, and it was evident that this technique could not be used to measure free hormone fractions if any of the protein-hormone complexes dissociated very rapidly. Nevertheless, important information was obtained using the charcoal technique. It was found that both cytosol and serum contain a number of sets of sites that bind thyroid hormone, some of which are saturable. However, the affinity of the saturable sites for both T4 and T3 is relatively low. The presence of alternative binding sites for excess hormone prevented any increase in the free fraction at high hormone concentrations. No evidence was obtained in either cytosol or serum of any high affinity, low capacity binding sites similar to those detected in tadpole liver nuclei. It is suggested that the binding of thyroid hormones in serum and liver cytosol in tadpoles serves a function other than the initiation of thyroid hormone action.