Bailly A, Savouret J F, Sallas N, Milgrom E
Eur J Biochem. 1978 Aug 1;88(2):623-32. doi: 10.1111/j.1432-1033.1978.tb12489.x.
Steroid-receptor complexes formed in concentrated cytosol at low temperature, low ionic strength and neutral pH are unable to bind to nuclei. Various procedures are known to promote their 'activation'. In the present work it is shown that an increase in temperature only enhances the rate of the reaction whereas no change in the equilibrium between activated and non-activated complexes is observed. On the contrary an increase in ionic strength or pH, as well as a removal of a low-molecular-weight inhibitor, not only accelerate the reaction but also increase the concentration of activated complexes at equilibrium. Using two steroids differing 3-fold in their affinity for the receptor, no difference was seen in the effect of the bound steroid on receptor activation. When combining various activation procedures it was observed that they acted independently of each other and additively. In all cases they retained their property of either modifying only the rate of the reaction or both its rate and equilibrium. Using changes in pH, it was also possible to induce shifts in the equilibrium between activated and non-activated complexes. After activation at pH 6.5, a first equilibrium was attained. When the pH was increased to 8 the equilibrium was displaced towards higher concentrations of activated complexes. A lowering of the pH resulted in a reversal of steroid-receptor complexes from the activated to the non-activated state. To clearly establish that this was not due to irreversible damage of the receptor, which would render it unable to bind to nuclei, it was shown that the complexes which had reverted to the non-activated state were still susceptible to activation. Regulatory events may thus exist which, for a given level of hormone and receptor, modulate the concentration of activated steroid-receptor complexes.
在低温、低离子强度和中性pH条件下于浓缩胞质溶胶中形成的类固醇-受体复合物无法与细胞核结合。已知多种方法可促进其“激活”。在本研究中表明，温度升高仅提高反应速率，而未观察到活化复合物与未活化复合物之间的平衡发生变化。相反，离子强度或pH升高以及去除低分子量抑制剂，不仅加速反应，还增加平衡时活化复合物的浓度。使用对受体亲和力相差3倍的两种类固醇，结合的类固醇对受体激活的影响未观察到差异。当组合各种激活方法时，发现它们彼此独立且具有加和作用。在所有情况下，它们要么仅改变反应速率，要么同时改变反应速率和平衡。利用pH变化，还可以诱导活化复合物与未活化复合物之间的平衡发生移动。在pH 6.5下激活后，达到第一个平衡。当pH升至8时，平衡向更高浓度的活化复合物方向移动。pH降低导致类固醇-受体复合物从活化状态逆转至未活化状态。为了明确这不是由于受体的不可逆损伤导致其无法与细胞核结合，研究表明恢复到未活化状态的复合物仍易于被激活。因此可能存在调节事件，对于给定水平的激素和受体，这些事件可调节活化类固醇-受体复合物的浓度。
