The myosin cross-bridge cycle and its control by twitchin phosphorylation in catch muscle
The myosin cross-bridge cycle and its control by twitchin phosphorylation in catch muscle
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DOI：
10.1016/s0006-3495(01)76024-9
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发表时间：
2001-01-01
影响因子：
3.4
通讯作者：
Siegman, MJ
中科院分区：
文献类型：
--
作者：
Butler, TM;Narayan, SR;Siegman, MJ
紫贻贝前足丝牵开肌的特点是肌球蛋白在捕捉过程中，紧张力的维持与能量利用率很低的状态。在pCa > 8的高力僵直中向透化肌肉添加MgATP导致一些力的快速损失，随后是非常缓慢的松弛速率，这是捕获的特征。在1 mM MgADP存在下，快组分减慢3-4倍，但快组分和慢组分（捕获）之间的分布不依赖于[MgADP]。tickin的磷酸化导致捕获组分的损失。不到4%的肌球蛋白头与ADP严格结合，并且无论抽搐是否磷酸化，从笼状ATP释放ATP后ADP形成的时间过程（0.2-10 s）都是相似的。这表明，MgATP结合到跨桥和随后的分裂是独立的tickin磷酸化，但脱离发生只有当tickin磷酸化。在AMP-PNP和ATP γ S中也观察到类似的脱附依赖于tickin磷酸化。结合ADP的单次转换实验表明，当通过tickin磷酸化释放捕获物时，ADP从横桥的释放速率增加，低[Ca 2 +]和未磷酸化的tickin似乎通过1）显著减缓连接的横桥ADP释放和2）防止ATP结合到僵直横桥后的分离。
The anterior byssus retractor muscle of Mytilus edulis was used to characterize the myosin cross-bridge during catch, a state of tonic force maintenance with a very low rate of energy utilization. Addition of MgATP to permeabilized muscles in high force rigor at pCa > 8 results in a rapid loss of some force followed by a very slow rate of relaxation that is characteristic of catch. The fast component is slowed 3-4-fold in the presence of 1 mM MgADP, but the distribution between the fast and slow (catch) components is not dependent on [MgADP]. Phosphorylation of twitchin results in loss of the catch component. Fewer than 4% of the myosin heads have ADP bound in rigor, and the time course (0.2-10 s) of ADP formation following release of ATP from caged ATP is similar whether or not twitchin is phosphorylated. This suggests that MgATP binding to the cross-bridge and subsequent splitting are independent of twitchin phosphorylation, but detachment occurs only if twitchin is phosphorylated. A similar dependence of detachment on twitchin phosphorylation is seen with AMP-PNP and ATP gammaS, Single turnover experiments on bound ADP suggest an increase in the rate of release of ADP from the cross-bridge when catch is released by phosphorylation of twitchin, Low [Ca2+] and unphosphorylated twitchin appear to cause catch by 1) markedly slowing ADP release from attached cross-bridges and 2) preventing detachment following ATP binding to the rigor cross-bridge.