Xu S G, Kress M, Huxley H E
J Muscle Res Cell Motil. 1987 Feb;8(1):39-54. doi: 10.1007/BF01767263.
Low-angle X-ray diffraction diagrams were obtained from chemically skinned frog sartorius muscles under low ionic strength relaxing conditions. Experiments on single muscle fibres from rabbit muscle and on muscle proteins in solution have suggested the presence of a 'low ionic strength attached state' of the myosin crossbridges to actin, in which the overall ATP splitting and force-generating cycle is still blocked. This opened up the possibility that structural information about one of the intermediate states in the crossbridge cycle might be obtained under these conditions. Using synchrotron radiation as a high intensity X-ray source we were able to record the appropriate diffraction diagrams with short exposure times and were able to compare the same muscles at normal and at low ionic strength. Changes in the intensities of the equatorial reflections an increase in the 143 A meridional intensity can be interpreted in a similar way. However, these attached bridges do not give rise to changes in the actin-based layer line reflections, nor is their presence associated with a weakening of the myosin layer line pattern. These results provide further evidence for the existence of bound states of crossbridges, in which their orientation relative to actin is not sharply defined.
在低离子强度松弛条件下，从化学去皮的青蛙缝匠肌获得了低角度X射线衍射图。对兔肌单肌纤维和溶液中的肌肉蛋白进行的实验表明，肌球蛋白横桥与肌动蛋白存在“低离子强度附着状态”，其中总的ATP分解和力产生循环仍然受阻。这就开启了在这些条件下可能获得有关横桥循环中间状态之一的结构信息的可能性。使用同步辐射作为高强度X射线源，我们能够在短曝光时间内记录适当的衍射图，并能够比较正常离子强度和低离子强度下的同一块肌肉。赤道反射强度的变化以及143埃子午强度的增加可以用类似的方式解释。然而，这些附着的桥不会引起基于肌动蛋白的层线反射的变化，它们的存在也与肌球蛋白层线图案的减弱无关。这些结果为横桥结合状态的存在提供了进一步的证据，在这种状态下，它们相对于肌动蛋白的取向没有明确定义。
