Effect of low pH on single skeletal muscle myosin mechanics and kinetics
Effect of low pH on single skeletal muscle myosin mechanics and kinetics
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DOI：
10.1152/ajpcell.00172.2008
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发表时间：
2008-07-01
影响因子：
5.5
通讯作者：
Warshaw, D. M.
中科院分区：
文献类型：
--
作者：
Debold, E. P.;Beck, S. E.;Warshaw, D. M.
酸中毒(低pH值)是肌肉疲劳的最古老的推定因素，但其抑制肌肉表现的分子机制仍未解决。为此，采用体外运动(IVM)和单分子激光捕获技术研究了低pH对鸡骨骼肌肌球蛋白分子力学和动力学的影响。在饱和ATP时，pH从7.4降至6.4，肌动蛋白细丝速度(V-肌动蛋白)减慢36%。单分子实验，在1MATP时，肌球蛋白的平均单位步长(D)从10+/-2 nm(pH 7.4)降低到2+/-1 nm(pH 6.4)。低pH条件下的单个结合事件与肌动球蛋白相互作用(平均d=10 nm)和非生产性(平均d=0 nm)相互作用的群体的存在是一致的。在pH 6.4时，将ATP浓度从1mM增加到1 mM，恢复了d(9+/-3 nm)，这表明非生产性相互作用的寿命仅取决于[ATP]。然而，在IVM测定中，提高[ATP](1-10 mM)并不能恢复Vactin，这表明低pH也延长了肌动蛋白的强结合(TON)。单分子实验中对TON的测定表明，酸中毒通过减慢ADP的释放速度延长了TON。因此，在分离受限的运动模型中(即，类似于d/ton的V-肌动蛋白)，ADP释放速度的减慢和非生产性肌球蛋白相互作用的存在可以解释酸中毒引起的Vactin的减少，这为肌肉疲劳的这一组成部分提供了分子解释。
Acidosis (low pH) is the oldest putative agent of muscular fatigue, but the molecular mechanism underlying its depressive effect on muscular performance remains unresolved. Therefore, the effect of low pH on the molecular mechanics and kinetics of chicken skeletal muscle myosin was studied using in vitro motility (IVM) and single molecule laser trap assays. Decreasing pH from 7.4 to 6.4 at saturating ATP slowed actin filament velocity (V-actin) in the IVM by 36%. Single molecule experiments, at 1 mu M ATP, decreased the average unitary step size of myosin (d) from 10 +/- 2 nm (pH 7.4) to 2 +/- 1 nm (pH 6.4). Individual binding events at low pH were consistent with the presence of a population of both productive (average d = 10 nm) and nonproductive (average d = 0 nm) actomyosin interactions. Raising the ATP concentration from 1 mu M to 1 mM at pH 6.4 restored d (9 +/- 3 nm), suggesting that the lifetime of the nonproductive interactions is solely dependent on the [ATP]. Vactin, however, was not restored by raising the [ATP] (1-10 mM) in the IVM assay, suggesting that low pH also prolongs actin strong binding (ton). Measurement of ton as a function of the [ATP] in the single molecule assay suggested that acidosis prolongs ton by slowing the rate of ADP release. Thus, in a detachment limited model of motility (i.e., V-actin similar to d/ton), a slowed rate of ADP release and the presence of nonproductive actomyosin interactions could account for the acidosis-induced decrease in Vactin, suggesting a molecular explanation for this component of muscular fatigue.