Negative cooperativity in the binding of thyroxine to human serum prealbumin. Preparation of tritium-labeled 8-anilino-1-naphthalenesulfonic acid.
Negative cooperativity in the binding of thyroxine to human serum prealbumin. Preparation of tritium-labeled 8-anilino-1-naphthalenesulfonic acid.
复制标题
甲状腺素与人血清前白蛋白结合的负协同作用。
作者：
R. N. Ferguson;H. Edelhoch;H. Saroff;J. Robbins;H. Cahnmann
在pH 7.4、0.05 M磷酸盐-0.10 M NaCl、25℃条件下，采用平衡透析法测定甲状腺素（T4）和8-苯胺-1-萘磺酸（ANS）与人血清白蛋白的结合。根据(1)两个独立位点和(2)两个负相互作用的相同位点的方程对数据进行了结合常数分析。通过独立位点模型评价得到的关联常数如下：对于T4结合，KT1 = 1.0 × 10-8 M-1, KT2 = 9.5 × 10-5 M-1；ANS结合KA1 = 9.5 × 10-5 M-1, KA2 = 2.1 × 10-5 M-1。相互作用模型给出了常数kT = 5.5 × 10-7 M-1和kA = 5.5 × 10-5 M-1。相互作用因子α，定义为α中的-RT为相互作用能量，对于T4和ANS， α T = 0.041, α A = 0.62。T4和ANS的“最佳拟合”值分别为2.0和1.6。T4与人前白蛋白的结合与ANS是竞争性的，从竞争实验中得到的结合常数与单独研究时得到的每个配体的结合常数一致。根据对人白蛋白前x射线数据的分析（Blake et al.），似乎有两个相同的T4位点。因此，很明显，T4的结合代表了一种负协同性的情况，这可能是由于配体之间的相互作用。
The binding of thyroxine (T4) and 8-anilino-1-naphthalenesulfonic acid (ANS) to human serum prealbumin was measured by equilibrium dialysis at pH 7.4 in 0.05 M phosphate-0.10 M NaCl at 25 degrees. The data were analyzed for the binding constants based on equations for (1) two independent sites and (2) two identical sites with negative interaction. Evaluation by the independent site model gave the following association constants: for T4 binding, KT1 = 1.0 x 10-8 M-1, KT2 = 9.5 x 10-5 M-1; for ANS binding, KA1 = 9.5 x 10-5 M-1, KA2 = 2.1 x 10-5 M-1. The interactive model gave constants kT = 5.5 x 10-7 M-1 and kA = 5.5 x 10-5 M-1. Interaction factors, alpha, defined such that -RT in alpha is the energy of interaction, were: alpha T = 0.041 AND ALPHA A = 0.62 for T4 and ANS, respectively. The "best fit" values for the number of sites were 2.0 and 1.6 for T4 and ANS, respectively. The binding of T4 to human prealbumin was competitive with ANS, and the binding constants evaluated from competition experiments were in agreement with those found for each ligand when studied separately. On the basis of analysis of X-ray data of human prealbumin (Blake et al.) there appear to be two identical T4 sites. It is therefore evident that the binding of T4 represents a case of negative cooperativity which is presumably due to interaction between ligands.