Some vertebrate muscles (e.g. those in bony fish) have a simple lattice A-band which is so well ordered that low-angle X-ray diffraction patterns are sampled in a simple way amenable to crystallographic techniques. Time-resolved X-ray diffraction through the contractile cycle should provide a movie of the molecular movements involved in muscle contraction. Generation of ‘Muscle—The Movie’ was suggested in the 1990s and since then efforts have been made to work out how to achieve it. Here we discuss how a movie can be generated, we discuss the problems and opportunities, and present some new observations. Low angle X-ray diffraction patterns from bony fish muscles show myosin layer lines that are well sampled on row-lines expected from the simple hexagonal A-band lattice. The 1st, 2nd and 3rd myosin layer lines at d-spacings of around 42.9 nm, 21.5 nm and 14.3 nm respectively, get weaker in patterns from active muscle, but there is a well-sampled intensity remnant along the layer lines. We show here that the pattern from the tetanus plateau is not a residual resting pattern from fibres that have not been fully activated, but is a different well-sampled pattern showing the presence of a second, myosin-centred, arrangement of crossbridges within the active crossbridge population. We also show that the meridional M3 peak from active muscle has two components of different radial widths consistent with (i) active myosin-centred (probably weak-binding) heads giving a narrow peak and (ii) heads on actin in strong states giving a broad peak.

中文翻译：

---

监测肌肉收缩时的肌球蛋白横桥循环：迈向“肌肉电影”。

一些脊椎动物的肌肉（例如硬骨鱼的肌肉）具有简单的晶格 A 带，该带非常有序，因此可以以适合晶体学技术的简单方式对低角度 X 射线衍射图样进行采样。通过收缩周期的时间分辨 X 射线衍射应该可以提供肌肉收缩中分子运动的影像。“肌肉电影”的产生是在 20 世纪 90 年代提出的，此后人们一直在努力研究如何实现它。在这里，我们讨论如何制作电影，讨论问题和机遇，并提出一些新的观察。硬骨鱼肌肉的低角度 X 射线衍射图显示，肌球蛋白层线在简单六边形 A 带晶格预期的行线上得到了很好的采样。d 间距分别约为 42.9 nm、21.5 nm 和 14.3 nm 的第 1、第 2 和第 3 肌球蛋白层线在来自活跃肌肉的模式中变弱，但沿层线存在采样良好的强度残余。我们在这里表明，来自破伤风平台的模式不是尚未完全激活的纤维的残余静息模式，而是一种不同的良好采样模式，显示活性纤维内存在第二个以肌球蛋白为中心的横桥排列。过桥人口。我们还表明，来自活跃肌肉的经向 M3 峰具有不同径向宽度的两个组成部分，这与 (i) 以活跃肌球蛋白为中心（可能是弱结合）的头给出窄峰和 (ii) 强状态下肌动蛋白上的头给出一致宽峰。