Factors contributing to troponin exchange in myofibrils and in solution.
Factors contributing to troponin exchange in myofibrils and in solution.
复制标题
影响肌原纤维和溶液中肌钙蛋白交换的因素。
DOI：
10.1023/a:1010300802980
复制
发表时间：
2000
影响因子：
2.7
通讯作者：
Chalovich,JM
中科院分区：
文献类型：
--
作者：
She,M;Trimble,D;Yu,LC;Chalovich,JM
肌纤维中的肌钙蛋白复合物可以通过温和的交换过程被外源性肌钙蛋白取代，其中肌动蛋白-原肌球蛋白复合物永远不会缺乏肌钙蛋白的完整补体（Brenneret al. (1999)Biophys J77:2677-2691）。这种交换过程的机制和影响这种交换的因素尚不清楚。在这项研究中，交换过程现已在肌原纤维和溶液中进行了检查。在严格条件下的肌原纤维中，当游离Ca2+浓度较低时，肌钙蛋白交换优先发生在肌动蛋白和肌球蛋白之间的重叠区域。当Ca2+浓度较高时，交换沿肌动蛋白均匀发生。Ca2+在溶液中也能促进肌钙蛋白的交换，但在溶液实验中还不能证实S1的作用。溶液中的交换速率对pH或离子强度的适度变化不敏感。温度每升高10°C，速率就会增加两倍。肌钙蛋白与肌动蛋白-原肌球蛋白结合的连续两步模型可以模拟观察到的结合和解离瞬态。在没有Ca2+或S1的情况下，k1= 7.12 μM−1s−1,k−1= 0.65 s−1,k2= 0.07 s−1,k−2= 0.0014 s−1。肌钙蛋白从肌动蛋白（k−2）分离的缓慢速度限制了溶液中的交换速率，并且很可能导致纤维中交换速率缓慢。
The troponin complex in a muscle fiber can be replaced with exogenous troponin by using a gentle exchange procedure in which the actin–tropomyosin complex is never devoid of a full complement of troponin (Brenneret al. (1999)Biophys J77:2677–2691). The mechanism of this exchange process and the factors that influence this exchange are poorly understood. In this study, the exchange process has now been examined in myofibrils and in solution. In myofibrils under rigor conditions, troponin exchange occurred preferentially in the region of overlap between actin and myosin when the free Ca2+concentration was low. At higher concentrations of Ca2+, the exchange occurred uniformly along the actin. Ca2+also accelerated troponin exchange in solution but the effect of S1 could not be confirmed in solution experiments. The rate of exchange in solution was insensitive to moderate changes in pH or ionic strength. Increasing the temperature resulted in a two-fold increase in rate with each 10°C increase in temperature. A sequential two step model of troponin binding to actin–tropomyosin could simulate the observed association and dissociation transients. In the absence of Ca2+or rigor S1, the following rate constants could describe the binding process:k1= 7.12 μM−1s−1,k−1= 0.65 s−1,k2= 0.07 s−1,k−2= 0.0014 s−1. The slow rate of detachment of troponin from actin (k−2) limits the rate of exchange in solution and most likely contributes to the slow rate of exchange in fibers.