Tanford C, Martin D W
Z Naturforsch C Biosci. 1982 May-Jun;37(5-6):522-6. doi: 10.1515/znc-1982-5-626.
This paper summarizes true equilibrium measurements for some partial reactions of the sarcoplasmic reticulum calcium pump transport cycle. The most important result is the estimation of the equilibrium constant for the interconversion of the two major conformational states of the protein, E (Ca2+ binding sites facing the cytoplasm) and E' (Ca2+ binding sides facing the sarcoplasmic reticulum lumen). The value of K0 = [E']/[E] cannot be evaluated directly by any method available at present, but observed cooperativity in the binding of Mg2+ and Ca2+ to unliganded protein strongly indicates that K0 much greater than 1. The most probable value, valid within an order of magnitude, is K0 congruent to 10(3), i.e., the E' state is more stable than the E state by about 4 kcal/mol.
本文总结了肌浆网钙泵转运循环中一些部分反应的真实平衡测量结果。最重要的结果是估算了蛋白质两种主要构象状态E（Ca2+结合位点面向细胞质）和E'（Ca2+结合位点面向肌浆网腔）相互转化的平衡常数。目前可用的任何方法都无法直接评估K0 = [E']/[E]的值，但观察到Mg2+和Ca2+与未结合配体的蛋白质结合时的协同作用强烈表明K0远大于1。最可能的值，在一个数量级范围内有效，是K0约为10(3)，即E'状态比E状态稳定约4千卡/摩尔。
