Activation of skeletal S-1 ATPase activity by actin-tropomyosin-troponin. Effect of Ca++ on the fluorescence transient.
Activation of skeletal S-1 ATPase activity by actin-tropomyosin-troponin. Effect of Ca++ on the fluorescence transient.
复制标题
肌动蛋白-原肌球蛋白-肌钙蛋白激活骨骼 S-1 ATP 酶活性。
DOI：
10.1016/s0006-3495(91)82065-3
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发表时间：
1991
影响因子：
3.4
通讯作者：
Chalovich,JM
中科院分区：
文献类型：
--
作者：
Stein,LA;Chalovich,JM
横纹肌的调节主要涉及细胞内游离钙浓度的变化对肌动蛋白-原肌球蛋白-肌钙蛋白复合体(以下简称[Acto]R)与肌动蛋白-原肌球蛋白-肌钙蛋白复合体(以下简称[Acto]R)相互作用的影响。在低钙浓度下，(Acto)R S-1与肌动蛋白R的结合几乎不受钙离子浓度的影响，但在高钙条件下，S-1与(Acto)R的结合速度可比高钙时低20倍。这意味着调控机制涉及肌动蛋白结合状态之间的动力学转换，而不是肌动蛋白结合变化的结果。在目前的工作中，我们研究了在低和高游离[Ca++]条件下，ATP结合和水解所产生的荧光瞬变。低游离[Ca++]时的这种转变幅度大于高游离[Ca++]时的转变幅度。在低游离[Ca~(++)]时，荧光瞬变速率随游离肌动蛋白浓度的增加而保持不变或略有下降，而在高游离[Ca~(++)]时，荧光瞬变速率随游离肌动蛋白浓度的增加而略有增加。观察到的利率变化还不够大，不足以产生监管重要性。荧光瞬变实验和稳态结合研究的结果也表明，M.ATP和M.ADP.PI与(肌动蛋白)R的结合都不是明显的钙敏感。这些数据表明，ATPase循环中的一个或多个额外步骤，即除了猝发转变之外，必须受钙的调节。
Regulation in striated muscles primarily involves the effect of changes in the free calcium concentration on the interaction of subfragment-1 (S-1) with the actin-tropomyosin-troponin complex (henceforth referred to as [acto]R). At low concentrations of free Ca++ the rate of ATP hydrolysis by (acto)R S-1 can be as much as 20-fold lower than that in the presence of high free Ca++, even though the binding of S-1 to (actin)R in the presence of ATP is virtually independent of the calcium concentration. This implies that the mechanism of regulation involves a kinetic transition between actin-bound states, rather than the result of changes in actin binding. In the current work, we have investigated the fluorescence transient that occurs with the binding and hydrolysis of ATP both at low and high free [Ca++]. The magnitude of this transition at low free [Ca++] is higher than at high free [Ca++]. At low free [Ca++], the rate of the fluorescence transient either stays constant or decreases slightly with increasing free actin concentrations, but at high free [Ca++] the rate increases slightly with increasing free actin concentration. The observed changes in rate are not great enough to be of regulatory importance. The results of the fluorescence transient experiments together with the binding studies performed at steady state also show that neither the binding of M.ATP or M.ADP.Pi to (actin)R is appreciably Ca++ sensitive. These data imply that an additional step (or steps) in the ATPase cycle, i.e., other than the burst transition, must be regulated by calcium.