Highsmith S, Murphy A J
Department of Biochemistry, School of Dentistry, University of the Pacific, San Francisco, California 94115.
Biochemistry. 1992 Jan 21;31(2):385-9. doi: 10.1021/bi00117a011.
The ionic strength dependence of the binding of rabbit skeletal muscle myosin subfragment 1, S1, to F-actin in the presence of saturating concentrations of MgATP or MgADP was analyzed in order to determine the association constants at zero ionic strength [K(0)] and the products of the net effective electric charges (magnitude of zMzA) at the binding interfaces. K(0) and magnitude of zM A were 1 x 10(6) M-1 and 17 esu2 for S1-MgADP,P, and 5 x 10(7) M-1 and 7 esu2 for S1-MgADP, respectively, for binding to F-actin at 25 degrees C. At ionic strengths near physiological, the increase in affinity is close to 10(4)-fold for this transition that may correspond to force generation in muscle fibers. The large, from 17 to 7 esu2, decrease in the electrostatic contribution to binding appears to be correlated with a much larger increase in nonelectrostatic interactions, unlike the simpler transition of actin-bound S1-MgADP to S1, which appears to be due entirely to electrostatic changes [Highsmith, S. (1990) Biochemistry 29, 10690-10694]. These results for acto-S1-MgADP,P to acto-S1-MgADP suggest that a substantial transformation of the actin binding site on S1 occurs even if there is a translocation to a new interface.
为了确定零离子强度下的缔合常数[K(0)]以及结合界面处净有效电荷的乘积（zM zA 的大小），分析了在饱和浓度的MgATP或MgADP存在下，兔骨骼肌肌球蛋白亚片段1（S1）与F-肌动蛋白结合的离子强度依赖性。在25℃下与F-肌动蛋白结合时，S1-MgADP，P的K(0)和zM zA 的大小分别为1×10⁶ M⁻¹ 和17 esu²，S1-MgADP的分别为5×10⁷ M⁻¹ 和7 esu²。在接近生理的离子强度下，这种转变的亲和力增加接近10⁴倍，这可能与肌纤维中的力产生相对应。与肌动蛋白结合的S1-MgADP到S1的较简单转变不同，后者似乎完全是由于静电变化[Highsmith, S. (1990) Biochemistry 29, 10690 - 10694]，结合的静电贡献从17 esu²大幅下降到7 esu²，这似乎与非静电相互作用的更大增加相关。从肌动蛋白-S1-MgADP，P到肌动蛋白-S1-MgADP的这些结果表明，即使存在向新界面的移位，S1上肌动蛋白结合位点也会发生实质性转变。
