Crepeau R H, McEwen B, Edelstein S J
Proc Natl Acad Sci U S A. 1978 Oct;75(10):5006-10. doi: 10.1073/pnas.75.10.5006.
Electron microscopic techniques have been used to reveal two classes of subunits of tubulin in ordered arrays. Presumably the two classes correspond to the alpha and beta polypeptide chains of tubulin that have been distinguished by chemical criteria. The two types of subunits alternate along individual protofilaments in microtubules, microtubule-precursor sheets, and extended zinc-tubulin sheets. The resolution of the two types of polypeptide chains is achieved by improved negative staining methods which produce micrographs with layer lines at 28 A(-1) and 84 A(-1) in optical or computed transforms, in addition to the layer lines at 21 A(-1) and 42 A(-1) described previously [Crepeau, R. H., McEwen, B., Dykes, G. & Edelstein, S. J. (1977) J Mol. Biol. 116, 301-315]. In microtubules or microtubule-precursor sheets, adjacent protofilaments are staggered by about 10 A, but parallel, in the sense that the alpha-beta vector points in the same direction for all of the protofilaments of the microtubule. However, for the sheets assembled in the presence of zinc, adjacent protofilaments are staggered by about 21 A and oriented in an antiparallel arrangement with alternate protofilaments related by a 2-fold screw axis. The antiparallel alignment of the protofilaments in the zinc-tubulin sheets accounts for their planarity (no tubular structures are found in the presence of moderate concentrations of zinc), since the intrinsic curvature found with parallel alignment of protofilaments in the absence of zinc would be cancelled by the antiparallel arrangement.
电子显微镜技术已被用于揭示微管蛋白的两类亚基呈有序排列。据推测，这两类亚基分别对应于通过化学标准区分的微管蛋白的α和β多肽链。这两种亚基类型沿着微管、微管前体片层以及延伸的锌 - 微管蛋白片层中的单个原纤维交替排列。通过改进的负染色方法实现了对这两种多肽链的分辨，除了先前描述的21 Å⁻¹和42 Å⁻¹的层线外，这些方法在光学或计算机变换中产生了28 Å⁻¹和84 Å⁻¹层线的显微照片[Crepeau, R. H., McEwen, B., Dykes, G. & Edelstein, S. J. (1977) J Mol. Biol. 116, 301 - 315]。在微管或微管前体片层中，相邻原纤维交错约10 Å，但相互平行，即α - β向量对于微管的所有原纤维都指向相同方向。然而，对于在锌存在下组装的片层，相邻原纤维交错约21 Å，并以反平行排列定向，交替的原纤维通过二重螺旋轴相关联。锌 - 微管蛋白片层中原纤维的反平行排列解释了它们的平面性（在中等浓度锌存在下未发现管状结构），因为在没有锌的情况下原纤维平行排列时发现的固有曲率会被反平行排列抵消。
