Wakabayashi K, Ueno Y, Amemiya Y, Tanaka H
Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University, Japan.
Adv Exp Med Biol. 1988;226:353-67.
X-ray diffraction studies of actin-containing thin filaments from frog skeletal muscles were done using a new type of integrating X-ray area detector (an imaging plate) and synchrotron radiation. The high sensitivity and wide dynamic range of the imaging plate made it possible to clearly record the weak thin filament pattern from a muscle during isometric contraction in less than 20 sec exposure time. The intensity distributions of the actin-based layer lines were measured. During contraction, most of the actin-based layer lines increased in intensity without noticeable changes of their layer-line profile and axial spacing in the resting state. The difference cylindrically symmetrical Patterson function was calculated using the intensity data of 15 actin-based layer lines. During contraction, the Patterson map was quite different from the rigor map and no significant indication of binding of the myosin heads was detected in the contracting map. This revealed that the labeling of myosin heads was not in accordance with the actin symmetry. Assuming that the intensity change during contraction is due to the structural change occurring within the thin filaments by the interaction with the myosin heads, model-calculating studies were done to interpret the intensity change. The observed intensity increase could be explained by changing the structure of the actin subunit and the position of tropomyosin molecules in the thin filament. With reference to the three-dimensional reconstructions of the thin filament electron micrographs, some models of the thin filament in the resting and contracting states were presented.
利用一种新型的积分式X射线面探测器（成像板）和同步辐射对青蛙骨骼肌中含肌动蛋白的细肌丝进行了X射线衍射研究。成像板的高灵敏度和宽动态范围使得在等长收缩过程中，能够在不到20秒的曝光时间内清晰记录来自肌肉的微弱细肌丝图案。测量了基于肌动蛋白的层线的强度分布。在收缩过程中，大多数基于肌动蛋白的层线强度增加，而其层线轮廓和静止状态下的轴向间距没有明显变化。利用15条基于肌动蛋白的层线的强度数据计算了差分圆柱对称帕特森函数。在收缩过程中，帕特森图与僵直图有很大不同，在收缩图中未检测到肌球蛋白头部结合的明显迹象。这表明肌球蛋白头部的标记与肌动蛋白的对称性不一致。假设收缩过程中的强度变化是由于细肌丝与肌球蛋白头部相互作用而发生的结构变化，进行了模型计算研究来解释强度变化。观察到的强度增加可以通过改变肌动蛋白亚基的结构和细肌丝中原肌球蛋白分子的位置来解释。参照细肌丝电子显微镜照片的三维重建，给出了静止和收缩状态下细肌丝的一些模型。
