Mendelson R A, Wilson M G
Biophys J. 1982 Aug;39(2):221-7. doi: 10.1016/S0006-3495(82)84511-6.
Fluorescence polarization and EPR experiments on azimuthally randomized helices bearing extrinsic (dipolar) probes yield information about the axial orientation and order of the probes. If the orientation of the probe on the structure bearing it is known and disorder is absent, the orientation of the structure may be ascertained. For cases where less probe orientation information is available and/or disorder is present, the available structural information is correspondingly reduced. Here we examine the available data on probes attached to cross-bridges in muscle fibers: four plausible cases of three-dimensional cross-bridge disorders are numerically modeled muscle in states of rigor and relaxation. In rigor, where the reported probe disorder is small (Thomas and Cooke, 1980), it was found that the cross-bridge disorder was also small. On the other hand, for the relaxed state where the probes are found to be completely disordered, the cross-bridges may have a considerable amount of order. This possibility is in concert with the results of x-ray diffraction, in which the presence of well-developed myosin-based layer lines indicates considerable order in relaxed muscle.
对带有外在（偶极）探针的方位随机螺旋进行荧光偏振和电子顺磁共振实验，可得出有关探针轴向取向和排列顺序的信息。如果已知探针在承载它的结构上的取向且不存在无序情况，则可以确定该结构的取向。对于探针取向信息较少和/或存在无序的情况，可用的结构信息相应减少。在这里，我们研究了附着在肌纤维横桥上的探针的现有数据：对三种三维横桥无序的合理情况进行了数值模拟，模拟了处于强直和松弛状态的肌肉。在强直状态下，据报道探针的无序程度较小（托马斯和库克，1980年），发现横桥的无序程度也较小。另一方面，对于发现探针完全无序的松弛状态，横桥可能具有相当程度的有序性。这种可能性与X射线衍射结果一致，在X射线衍射中，发达的基于肌球蛋白的层线的存在表明松弛肌肉中存在相当程度的有序性。
