Levine R J, Kensler R W, Reedy M, Hoffman W, Davidheiser S, Davies R E
Adv Exp Med Biol. 1984;170:93-106. doi: 10.1007/978-1-4684-4703-3_9.
We have demonstrated remarkable similarity among the skeletal muscles of chelicerate arthropods with respect to the cross-bridge arrangement on the surface of their thick filaments. The latter, gently isolated from the muscles of three representative species (Limulus telson , tarantula leg and scorpion leg and tail) have been examined by electron microscopy and optical diffraction using both negatively stained and unidirectionally metal shadowed preparations. The filaments are highly periodic and produce clear and detailed diffraction patterns. The cross-bridge projections form integral surface helices, with an axial spacing of 14.5 nm between adjacent crowns and a major axial repeat every 43.5 nm. We have demonstrated previously that Limulus filaments are four-stranded and analysis of both electron micrographs and their transforms, as well as optical reconstructions of the arachnid filaments is consistent with their also having a four-start surface helix, which is right-handed in all cases. Of all those examined, thus far, only Limulus thick filaments have been demonstrated to change length under various conditions. Shortened Limulus filaments isolated from K+-stimulated fibers retain the 43.5 nm axial repeat periodicity and 14.5 nm axial spacing between crowns. In preliminary analysis of negatively stained and metal shadowed preparations, we see no systematic change with respect to screw or rotational symmetry in short as compared with long filaments. A few of the former have a very slightly increased diameter (3-4 nm) in the middle of each filament arm. This region often shows disorder on optical transforms. From our results we cannot rule out the possibility that disaggregation and reaggregation of thick filament proteins accompany the changes in length of Limulus thick filaments.
我们已经证明，螯肢类节肢动物的骨骼肌在粗肌丝表面的横桥排列方面具有显著的相似性。从三种代表性物种（鲎的尾节、狼蛛腿以及蝎子腿和尾巴）的肌肉中轻柔分离出的粗肌丝，已经通过电子显微镜和光学衍射进行了检查，使用了负染色和单向金属投影制备方法。这些肌丝具有高度周期性，并产生清晰且详细的衍射图案。横桥突起形成完整的表面螺旋，相邻冠之间的轴向间距为14.5纳米，每43.5纳米有一个主要的轴向重复。我们之前已经证明鲎的肌丝是四股的，对电子显微镜图像及其变换的分析，以及蛛形纲动物肌丝的光学重建，都与它们也具有四起始表面螺旋一致，在所有情况下都是右手螺旋。在迄今为止检查的所有样本中，只有鲎的粗肌丝被证明在各种条件下会改变长度。从钾离子刺激的纤维中分离出的缩短的鲎肌丝保留了43.5纳米的轴向重复周期性以及冠之间14.5纳米的轴向间距。在对负染色和金属投影制备样本的初步分析中，我们发现与长肌丝相比，短肌丝在螺旋或旋转对称性方面没有系统性变化。其中一些短肌丝在每个肌丝臂的中间直径略有增加（3 - 4纳米）。这个区域在光学变换中常常显示出无序。从我们的结果来看，我们不能排除鲎粗肌丝长度变化伴随着粗肌丝蛋白解聚和重新聚集的可能性。
