Increase in binding capacity for triiodothyronine in tadpole tail nuclei during metamorphosis
Increase in binding capacity for triiodothyronine in tadpole tail nuclei during metamorphosis
复制标题
变态过程中蝌蚪尾核对三碘甲状腺原氨酸的结合能力增加
作者：
K. Yoshizato;E. Frieden
蝌蚪尾部的回归受到甲状腺激素的直接控制，并为研究其作用机制提供了一个系统1。在该系统中，三碘甲状腺原氨酸 (T3) 在引起尾部退化方面的活性是甲状腺素 (T4) 的两到五倍2,3。对激素与切片尾鳍组织孵育后 125I-T3 和 125I-T4 结合的研究揭示了细胞核中的高亲和力、可饱和结合位点 4——T3 和 T4 每个核最多分别有 1,500 个和 800 个位点。 （蝌蚪肝细胞也获得了类似的结果5。）T3 和 T4 的解离常数几乎相同 (10−10 M)。这些结果表明，在两栖动物中，与 T3 和 T4 的生物活性相关的是结合位点的最大数量，而不是亲和常数。然而，在哺乳动物中，在细胞核 6-8 中发现了甲状腺激素的特定高亲和力结合位点，并且与亲和力常数相关。
REGRESSION of the tadpole tail is under direct control of the thyroid hormones and provides a system for study of their mechanism of action1. In this system triiodothyronine (T3) is two to five times as active as thyroxine (T4) in causing tail regression2,3. Studies of the binding of 125I-T3 and 125I-T4 after incubation of hormone with sliced tailfin tissues have revealed high-affinity, saturable binding sites in the cell nucleus4—a maximum of 1,500 and 800 sites per nucleus for T3 and T4, respectively. (Similar results have been obtained with tadpole liver cells5.) The dissociation constants for T3 and T4 were almost identical (10−10 M). These results suggest that in amphibians the maximum number of binding sites rather than the affinity constant correlate with the biological activity of T3 and T4. In mammals, however, specific high-affinity binding sites for the thyroid hormones were found in nuclei6–8 and correlate with the affinity constant.