Time-resolved X-ray diffraction studies of myosin head movements in live frog sartorius muscle during isometric and isotonic contractions
Time-resolved X-ray diffraction studies of myosin head movements in live frog sartorius muscle during isometric and isotonic contractions
复制标题
等长收缩和等张收缩期间活青蛙缝匠肌肌球蛋白头部运动的时间分辨 X 射线衍射研究
DOI：
10.1007/bf00123484
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发表时间：
1994
影响因子：
2.7
通讯作者：
E. Towns
中科院分区：
文献类型：
--
作者：
M. Martin;J. Bordas;G. Diakun;J. Harries;J. Lowy;G. Mant;A. Svensson;E. Towns
摘要
利用达累斯伯里同步辐射源的设备，在约8°C的条件下，以2毫秒或4毫秒的时间分辨率记录了肌肉的子午线衍射图案。在等长收缩中，强直峰值张力（P₀）在约400毫秒时达到。在这种情况下，从静止状态受到刺激后，主要反射（38.2纳米的肌钙蛋白反射，以及21.5纳米和14.34/14.58纳米的肌球蛋白反射）变化的时间可以用四种类型的时间进程来解释：K₁、K₂、K₃和K₄。K₁在刺激后立即开始，但K₂、K₃和K₄的开始延迟了约16毫秒的潜伏期。相对于各自潜伏期的结束，K₁、K₂、K₃和K₄的半衰期分别为14 - 16毫秒、16毫秒、32毫秒和52毫秒。在半衰期方面，K₁、K₂、K₃分别比张力上升提前52毫秒、36毫秒和20毫秒。K₄与张力上升的时间进程平行。通过对数据的分析，我们得出结论：K₁反映了涉及肌钙蛋白系统的细丝激活；K₂源于有序 - 无序转变，在此过程中细丝之间的配准丢失；K₃是由于肌动 - 肌球蛋白复合物的形成，在P₀时，该复合物导致70%或更多的头部以基于肌动蛋白的周期性进行衍射；K₄是由肌球蛋白头部轴向取向的变化引起的（相对于细丝轴），据估计从静止时的65 - 70°变化到P₀时的约90°。等张收缩实验表明，在约0.27P₀的负荷下缩短期间，至少85%的头部（相对于在P₀时形成肌动 - 肌球蛋白复合物的那些头部）以基于肌动蛋白的周期性进行衍射，而它们的轴向取向与静止时相比没有变化。在可忽略不计的负荷下缩短期间，至多5 - 10%的头部（相对于在P₀时形成肌动 - 肌球蛋白复合物的那些头部）以基于肌动蛋白的周期性进行衍射，并且它们的轴向取向也与静止时相同。这表明在等长收缩中，轴向取向的变化不是主动张力产生的原因，而是其结果。对数据的分析表明，与负荷无关，大多数循环头部执行的异步轴向运动的幅度比静止时大不超过0.5 - 0.65纳米。为了根据传统的倾斜头部模型解释衍射数据，人们必须假设少数头部和/或它们质量的一小部分执行该模型所要求的大得多的运动。因此我们得出结论，要么我们的图案中没有所需的信息，要么必须提出一种关于收缩的替代假设。
SummaryUsing the facilities at the Daresbury Synchrotron Radiation Source, meridional diffraction patterns of muscles at ca 8°C were recorded with a time resolution of 2 or 4 ms. In isometric contractions tetanic peak tension (P0) is reached in ca 400 ms. Under such conditions, following stimulation from rest, the timing of changes in the major reflections (the 38.2 nm troponin reflection, and the 21.5 and 14.34/14.58 nm myosin reflections) can be explained in terms of four types of time courses: K1, K2, K3 and K4. The onset of K1 occurs immediately after stimulation, but that of K2, K3 and K4 is delayed by a latent period of ca 16 ms. Relative to the end of their own latent periods the half-times for K1, K2, K3 and K4 are 14–16, 16, 32 and 52 ms, respectively. In half-times, K1, K2, K3 lead tension rise by 52, 36 and 20 ms, respectively. K4 parallels the time course of tension rise. From an analysis of the data we conclude that K1 reflects thin filament activation which involves the troponin system; K2 arises from an order-disorder transition during which the register between the filaments is lost; K3 is due to the formation of an acto-myosin complex which (at P0) causes 70% or more of the heads to diffract with actin-based periodicities; and K4 is caused by a change in the axial orientation of the myosin heads (relative to thin filament axis) which is estimated to be from 65–70° at rest to ca 90° at P0. Isotonic contraction experiments showed that during shortening under a load of ca 0.27 P0, at least 85% of the heads (relative to those forming an acto-myosin complex at P0) diffract with actin-based periodicities, whilst their axial orientation does not change from that at rest. During shortening under a negligible load, at most 5–10% of the heads (relative to those forming an acto-myosin complex at P0) diffract with actin-based periodicities, and their axial orientation also remains the same as that at rest. This suggests that in isometric contractions the change in axial orientation is not the cause of active tension production, but rather the result of it. Analysis of the data reveals that independent of load, the extent of asynchronous axial motions executed by most of the cycling heads is no more than 0.5–0.65 nm greater than at rest. To account for the diffraction data in terms of the conventional tilting head model one would have to suppose that a few of the heads, and/or a small part of their mass perform the much larger motions demanded by that model. Therefore we conclude either that the required information is not available in our patterns or that an alternative hypothesis for contraction has to be developed.
通过电子显微镜直接观察肌动球蛋白三磷酸酶循环中弱结合的中间体。
影响因子：
3.4
作者：
Pollard,TD;Bhandari,D;Maupin,P;Wachsstock,D;Weeds,AG;Zot,HG
通讯作者：
Zot,HG