Interference fine structure and sarcomere length dependence of the axial x-ray pattern from active single muscle fibers
Interference fine structure and sarcomere length dependence of the axial x-ray pattern from active single muscle fibers
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DOI：
10.1073/pnas.97.13.7226
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发表时间：
2000-06-20
影响因子：
11.1
通讯作者：
Lombardi, V
中科院分区：
文献类型：
--
作者：
Linari, M;Piazzesi, G;Lombardi, V
在欧洲同步辐射装置上，用高度准直的X射线束记录了青蛙骨骼肌单个完整纤维的轴向X射线衍射图。在肌节长度为2.2-3.2微米的等长收缩过程中，与肌球蛋白头沿肌丝重复有关的M3X射线反射被分解为两个峰。M3总强度随肌节长度的增加呈线性下降，并与肌球蛋白与肌动蛋白细丝的重叠度成正比，表明其来自重叠区的肌球蛋白头。肌节长度越长，M3峰之间的间隔越小，这可以通过每个肌节两个重叠区肌球蛋白头部之间的X射线干涉来定量解释。M3峰的相对强度与肌节长度无关，表明在肌球蛋白主动收缩过程中，肌球蛋白细丝的非重叠区和重叠区的轴向周期相同，为14.57 nm。在静息纤维中，这一周期为14.34 nm，因此肌肉激活会导致肌球蛋白细丝结构在不重叠部分和重叠部分发生变化。这一结果为研究肌球蛋白头部在肌肉收缩过程中的运动提供了一种新的工具，具有前所未有的空间分辨率。
Axial x-ray diffraction patterns from single intact fibers of frog skeletal muscle were recorded by using a highly collimated x-ray beam at the European Synchrotron Radiation Facility. During isometric contraction at sarcomere lengths 2.2-3.2 mu m, the M3 x-ray reflection, associated with the repeat of myosin heads along the filaments, was resolved into two peaks. The total M3 intensity decreased linearly with increasing sarcomere length and was directly proportional to the degree of overlap between myosin and actin filaments, showing that it comes from myosin heads in the overlap region. The separation between the M3 peaks was smaller at longer sarcomere length and was quantitatively explained by x-ray interference between myosin heads in the two overlap regions of each sarcomere. The relative intensity of the M3 peaks was independent of sarcomere length, showing that the axial periodicities of the nonoverlap and overlap regions of the myosin filament have the same value, 14.57 nm, during active contraction. In resting fibers the periodicity is 14.34 nm, so muscle activation produces a change in myosin filament structure in the nonoverlap as well as the overlap part of the filament. The results establish x-ray interferometry as a new tool for studying the motions of myosin heads during muscle contraction with unprecedented spatial resolution.