X-Ray Diffraction Studies on Structural Changes of Actin-Containing Thin Filaments during Contraction of Skeletal Muscles

用同步辐射对蛙骨骼肌肌动蛋白5.9 nm和5.1 nm层线进行了同步辐射时间分辨X射线衍射研究。这些肌动蛋白层线的积分强度在破伤风期间增加了30-50%，其中5.9 nm反射增加了30-50%，5.1 nm反射增加了约70%。这两种反射的强度增量都大于静止状态向僵硬状态转变时的强度增量。5.9 nm反射的强度变化先于肌球蛋白42.9 nm的子午线外反射、赤道反射和等长张力。在肌肉收缩过程中，5.9 nm层线的强度分布与在僵硬状态下观察到的不同。一种新型的积分面X射线探测器(成像板)被用于肌肉收缩的衍射研究。成像板的高灵敏度和宽动态范围大大缩短了曝光时间，使得使用同步辐射从收缩的青蛙骨骼肌记录到非常清晰的二维X射线衍射图成为可能，轴向间距高达2.0 nm，仅需10秒。在蛙骨骼肌收缩过程中，大多数肌动蛋白层线的强度增加，其峰值位置沿层线和轴向间距没有明显变化。测量了肌动蛋白层线的层线强度分布。通过模型计算进行了结构分析，得到了与观测强度最好的拟合度。结果表明，在收缩过程中，原肌球蛋白分子与肌球蛋白头部的相互作用以及钙离子与肌钙蛋白的结合都会引起肌动蛋白亚基结构的改变和原肌球蛋白分子的位置变化。

Time-resolved X-ray diffraction studies have been made on the 5.9 nm and 5.1 nm actin layer lines from frog skeletal muscles during an isometric tetanus, using synchrotron radiation. The integrated intensities of these actin layer lines were found to increase during a tetanus by 30-50% for the 5.9 nm reflection and about 70% for the 5.1 nm reflection of the resting values. The intensity increase of both reflections was greater than that taking place in the transition from rest to rigor state. The intensity change of the 5.9 nm reflection preceded those of the myosin 42.9 nm off-meridional reflection and equatorial reflections, as well as the isometric tension. The intensity profile of the 5.9 nm layer line during contraction was found to be different from that observed in the rigor state.A conceptually new type of an integrating area X-ray detector (an imaging plate) was used in a diffraction study of muscle contraction. The high sensitivity and wide dynamic range of the imaging plate resulted in a dramatic reduction in the exposure time, making it possible to record very clear two-dimensional X-ray diffraction patterns of up to 2.0 nm axial spacing from a contracting frog skeletal muscle as little as 10 seconds using synchrotron radiation. During contraction of a frog skeletal muscle, most of actin layer lines increased in intensity without noticeasble changes in their peak positions along the layer line and axial spacing. The layer-line intensity distributions of actin layer lines were measured. The structural analyses were made by model-calculation to obtain the best-fit to the observed intensities. The results indicated that during contraction the changes of the domain structure in the actin subunit as well as the positional change of tropomyosin molecules take place by the interaction with myosin heads as well as the binding of Ca ions to troponin.