Schmitz H, Lucaveche C, Reedy M K, Taylor K A
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710.
Biophys J. 1994 Oct;67(4):1620-33. doi: 10.1016/S0006-3495(94)80635-6.
In this work we examined the arrangement of cross-bridges on the surface of myosin filaments in the A-band of Lethocerus flight muscle. Muscle fibers were fixed using the tannic-acid-uranyl-acetate, ("TAURAC") procedure. This new procedure provides remarkably good preservation of native features in relaxed insect flight muscle. We computed 3-D reconstructions from single images of oblique transverse sections. The reconstructions reveal a square profile of the averaged myosin filaments in cross section view, resulting from the symmetrical arrangement of four pairs of myosin heads in each 14.5-nm repeat along the filament. The square profiles form a very regular right-handed helical arrangement along the surface of the myosin filament. Furthermore, TAURAC fixation traps a near complete 38.7 nm labeling of the thin filaments in relaxed muscle marking the left-handed helix of actin targets surrounding the thick filaments. These features observed in an averaged reconstruction encompassing nearly an entire myofibril indicate that the myosin heads, even in relaxed muscle, are in excellent helical register in the A-band.
在这项研究中，我们研究了田鳖飞行肌A带中肌球蛋白丝表面横桥的排列。使用单宁酸 - 醋酸铀（“TAURAC”）程序固定肌肉纤维。这种新程序能显著良好地保存松弛昆虫飞行肌的天然特征。我们从倾斜横切面的单张图像计算三维重建。重建结果显示，在横截面视图中，平均肌球蛋白丝呈方形轮廓，这是由于沿着丝每14.5纳米重复单元中四对肌球蛋白头部的对称排列所致。这些方形轮廓沿着肌球蛋白丝表面形成非常规则的右手螺旋排列。此外，TAURAC固定在松弛肌肉中捕获了近完整的38.7纳米细肌丝标记，标记了围绕粗肌丝的肌动蛋白靶标的左手螺旋。在涵盖几乎整个肌原纤维的平均重建中观察到的这些特征表明，即使在松弛肌肉中，肌球蛋白头部在A带中也处于极佳的螺旋对齐状态。
