Savu L, Vranckx R, Maya M, Nunez E A
U.224, INSERM, Faculté de Médecine Xavier Bichat, Paris, France.
Biochem Biophys Res Commun. 1989 Mar 31;159(3):919-26. doi: 10.1016/0006-291x(89)92196-7.
We use gel equilibration and electrophoretic techniques to compare the binding properties of thyroxine binding globulin and thyroxine binding prealbumin in rat sera. The evidence indicates that TBG bears the serum lowest capacity highest affinity sites for thyroxine (T4) and triiodothyronine (T3) (Ka1 greater than or equal to 10(9) M-1) as well as weaker saturable T3 sites (Ka2 approximately 10(8) M-1). TBPA bears for T4 only Ka2 approximately 10(8) M-1 sites and for T3 only Ka approximately 10(6) M-1 sites. Consistent with these parameters are the specific responses of TBG and TBPA binding activities to varying serum concentrations of T4, T3, oleic acid, the drugs diphenylhydantoin or salicylate. The primary attack of these compounds is aimed at TBG. Small T4, oleate or DPH doses chase the TBG-bound T4 to TBPA, high doses of T4 or oleate but not of DPH inhibiting the T4 binding to both proteins. In the T3-serum interactions, all tested compounds displace the TBG-bound hormone without chasing it to TBPA. The high reactivity of TBG sites designates the protein as crucially involved in modulating the free vs bound serum levels of T4 and T3 against physiological or pathological variations of binding competitors.
我们运用凝胶平衡和电泳技术来比较大鼠血清中甲状腺素结合球蛋白（TBG）和甲状腺素结合前白蛋白（TBPA）的结合特性。证据表明，TBG对甲状腺素（T4）和三碘甲状腺原氨酸（T3）具有血清中最低容量但最高亲和力的位点（Ka1大于或等于10⁹ M⁻¹），以及较弱的可饱和T3位点（Ka2约为10⁸ M⁻¹）。TBPA仅对T4具有Ka2约为10⁸ M⁻¹的位点，对T3仅具有Ka约为10⁶ M⁻¹的位点。与这些参数一致的是，TBG和TBPA的结合活性对血清中不同浓度的T4、T3、油酸、药物苯妥英或水杨酸盐有特异性反应。这些化合物的主要作用靶点是TBG。小剂量的T4、油酸或苯妥英会将与TBG结合的T4转移至TBPA，高剂量的T4或油酸而非苯妥英会抑制T4与这两种蛋白质的结合。在T3与血清的相互作用中，所有测试化合物都会取代与TBG结合的激素，而不会将其转移至TBPA。TBG位点的高反应性表明该蛋白质在针对结合竞争物的生理或病理变化调节血清中游离与结合的T4和T3水平方面起着关键作用。
