Lymn R W
Biophys J. 1978 Jan;21(1):93-8. doi: 10.1016/S0006-3495(78)85510-6.
The characteristic equatorial X-ray pattern from a relaxed vertebrate skeletal muscle changes when the muscle is activated. In particular, there is a simultaneous decrease in the intensity of the first reflection (I10) and increase in the intensity of the second (I11). This observed change is almost reciprocal. When compared with the predictions of computer modeling, it produces a strong argument that the intensity change is due to a redistribution of myosin heads (myosin subfragment-1 or S-1), which results from the formation and configuration changes of actin-myosin links. Computer modeling shows that different actin-S-1 configurations will give different numerical values for I10 and I11, assuming the same number of attachments. For a given configuration, the intensity changes are a nonlinear function of attachment number, so that direct scaling of force to reflection intensity may be difficult. Data from active muscle are consistent with the notion that in different states of active muscle, i.e. shortening or isometric, there are different average configurations of actin-myosin attachment and different numbers of actin-myosin links.
当脊椎动物骨骼肌被激活时，其松弛状态下特有的赤道面X射线图谱会发生变化。具体而言，一级反射（I10）的强度会同时降低，而二级反射（I11）的强度会增加。观察到的这种变化几乎是相互的。与计算机模拟的预测结果相比，这有力地证明了强度变化是由于肌球蛋白头部（肌球蛋白亚片段-1或S-1）的重新分布，这是由肌动蛋白-肌球蛋白连接的形成和构象变化导致的。计算机模拟表明，假设附着数量相同，不同的肌动蛋白-S-1构象会给出不同的I10和I11数值。对于给定的构象，强度变化是附着数量的非线性函数，因此将力直接按比例缩放至反射强度可能会很困难。来自活动肌肉的数据与以下观点一致：在活动肌肉的不同状态下，即缩短或等长状态下，肌动蛋白-肌球蛋白附着的平均构象不同，肌动蛋白-肌球蛋白连接的数量也不同。
