Lowy J, Poulsen F R
Open University Research Unit, Oxford, United Kingdom.
Biophys J. 1990 May;57(5):977-85. doi: 10.1016/S0006-3495(90)82617-5.
Using x-rays from synchrotron radiation, we studied diffuse scattering, sometimes together with the myosin layer lines. With an area detector, sartorius muscles and a time resolution of 150 ms, earlier results from semitendinosus muscles contracting isometrically at 6 degrees C (Lowy, J., and F. R. Poulsen. 1987. J. Mol. Biol. 194:595-600) were confirmed and extended. Evidence from intensity changes both in the diffuse scattering and in the myosin layer lines showed that the majority of the heads become disordered at peak tetanic tension. With a linear detector and a time resolution of 5 ms, it was found that during tension rise the intensity increase of the diffuse scattering (which amounted maximally to 12% recorded near the meridian) runs approximately 20 ms ahead of the mechanical change, comparing half-completion times. This suggests that an appreciable number of heads change orientation before peak tension is reached. In quick release experiments the diffuse scattering intensity showed very little change. Recorded near the meridian during rapid shortening, however, it decreased progressively with a half-time of approximately 40 ms. This change amounted to approximately 35% of that observed during the initial tension rise. We interpret this to indicate that during rapid shortening a certain number of heads assume an orientation characteristic of the relaxed state. Viewed in the context of the behavior of the first myosin layer line and the (1, 1) equatorial reflection in similar experiments (Huxley, H. E., M. Kress, A. R. Faruqi, and R. M. Simmons. 1988. Molecular Mechanism of Muscle Contraction), the present results provide further support for the view that the diffuse scattering is mostly due to disordered myosin heads; whilst ordered heads produce the myosin layer lines (Poulsen, F. R., and J. Lowy.1983. Nature lLond.l. 303:146-152).
利用同步辐射产生的X射线，我们研究了漫散射，有时还结合肌球蛋白层线进行研究。使用面积探测器、缝匠肌以及150毫秒的时间分辨率，对半腱肌在6摄氏度下等长收缩的早期研究结果（Lowy, J., and F. R. Poulsen. 1987. J. Mol. Biol. 194:595 - 600）得到了证实和扩展。漫散射和肌球蛋白层线强度变化的证据表明，在强直收缩张力峰值时，大多数头部变得无序。使用线性探测器和5毫秒的时间分辨率发现，在张力上升过程中，漫散射强度的增加（在子午线附近记录到的最大增加量为12%）在比较半完成时间时，比机械变化提前约20毫秒。这表明在达到张力峰值之前，相当数量的头部会改变方向。在快速释放实验中，漫散射强度变化很小。然而，在快速缩短过程中于子午线附近记录时，它以约40毫秒的半衰期逐渐下降。这种变化量约为初始张力上升期间观察到的变化量的35%。我们将此解释为表明在快速缩短过程中，一定数量的头部呈现出松弛状态的特征取向。从类似实验中第一条肌球蛋白层线和（1, 1）赤道反射的行为背景来看（Huxley, H. E., M. Kress, A. R. Faruqi, and R. M. Simmons. 1988. Molecular Mechanism of Muscle Contraction），目前的结果进一步支持了这样一种观点，即漫散射主要是由于无序的肌球蛋白头部引起的；而有序的头部产生肌球蛋白层线（Poulsen, F. R., and J. Lowy.1983. Nature lLond.l. 303:146 - 152）。
