Evidence from electron microscope studies on actin paracrystals concerning the origin of the cross-striation in the thin filaments of vertebrate skeletal muscle
Evidence from electron microscope studies on actin paracrystals concerning the origin of the cross-striation in the thin filaments of vertebrate skeletal muscle
复制标题
电子显微镜对肌动蛋白副晶体研究的证据，涉及脊椎动物骨骼肌细丝中交叉条纹的起源
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发表时间：
1973
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通讯作者：
E. J. Hanson
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作者：
E. J. Hanson
当纯化的F-肌动蛋白被Mg 2+沉淀时，它形成由规则堆积的细丝组成的准晶体，这些细丝保留肌动蛋白聚合物的双螺旋结构特征。在负染色的标本中，唯一观察到的轴向周期性是肌动蛋白聚合物的周期性。在切片中，聚合物结构未解析，次晶未出现横纹。由未纯化的肌动蛋白制备物形成的次晶体同样含有规则排列的细丝，其中观察到F-肌动蛋白结构，但此外，细丝的组装以相当规则的间隔（约37 nm）被未染色的无定形材料的条带穿过。这些次晶的切片显示出相应的横纹（平均间距38 nm）。其他已知存在于未纯化的肌动蛋白制剂中的蛋白质分别制备并加入到纯化的F-肌动蛋白溶液中;在Mg 2+沉淀时形成准晶体。当将原肌球蛋白和肌钙蛋白的混合物添加到肌动蛋白中时，就会再现交叉条纹。单独添加纯化的原肌球蛋白导致缺乏横纹的次晶。横条纹在次晶体中的肌原纤维的细丝组装（如在切片和负染色的I-段中所见）的比较支持这样的结论，即类似于天然的细丝已从肌动蛋白，原肌球蛋白和肌钙蛋白复合物合成。因此，细肌丝中的横纹可归因于肌钙蛋白复合物的部分或全部位于沿肌丝以规则间隔沿着分布的部位。
When purified F-actin is precipitated by Mg2+, it forms paracrystals consisting of regularly packed filaments that retain the double-helical structure characteristic of actin polymers. In negatively stained preparations the only axial periodicity observed is that of the actin polymers. In sections, the polymer structure is not resolved and the paracrystals do not appear cross-striated. The paracrystals formed from unpurified actin preparations likewise contain regularly packed filaments in which the F-actin structure is observed but, in addition, the assembly of filaments is crossed at fairly regular intervals (approximately 37 nm) by bands of unstained amorphous material. Sections of these paracrystals show a corresponding cross-striation (mean spacing 38 nm). Other proteins known to be present in unpurified preparations of actin were prepared separately and added in solution to purified F-actin; paracrystals were formed on Mg2+ precipitation. The cross-striation was reproduced when a mixture of tropomyosin and troponin had been added to the actin. The addition of purified tropomyosin alone resulted in paracrystals that lacked the cross-striation. Comparison of the cross-striation in the paracrystals with that in the thin filament assembly of the myofibril (as seen in sections and in negatively stained I-segments) supports the conclusion that filaments resembling the natural ones have been synthesized from actin, tropomyosin and the troponin complex. It follows that the cross-striation in the thin myofilaments can be attributed to the location of part or all of the troponin complex at sites spaced at regular intervals along the filaments.