Properties of the high-molecular-weight protein (spectrin) from human-erythrocyte membranes.
Properties of the high-molecular-weight protein (spectrin) from human-erythrocyte membranes.
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人红细胞膜高分子量蛋白（血影蛋白）的特性。
DOI：
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发表时间：
1975
期刊：
影响因子：
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通讯作者：
G. H. Beaven
中科院分区：
文献类型：
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作者：
W. Gratzer;G. H. Beaven
从人红细胞中分离出高分子量蛋白组分，并对其溶解度进行了研究。在生理溶剂条件下，光谱不聚集，不受影响，无论是在流体力学性质和构象上，通过圆二色性和固有荧光来判断，通过添加钙离子。当pH值降低时，乳白色首先出现，这对应于蛋白质的相关纤维状态，当达到临界pH值时，沉淀随之而来。沉淀剖面的特点是极端尖锐，在多酸-多碱混合物或多两性的相分离中观察到的那种。钙离子的加入使沉淀边缘向更高的ph偏移。钠离子也有类似的作用，但效果较小。在老化的光谱制剂或冰冻红细胞幽灵制剂中，轮廓的位置明显移位。新制备的光谱剂主要由9.7 S的组分沉积组成，4.4 S的少量组分（以及高团聚体的痕迹）。这种模式与离子强度无关，也与钙离子的存在与否无关。这种小成分的比例随着时间的推移而增加，在用冰冻的鬼魂制作幽灵的制剂中，它总是占主导地位。在盐酸胍的低浓度下，较大的组分逐渐被较小的组分所取代，当变性剂的浓度达到1m时，这两种组分完全消失。在低于1m的浓度下，这两种组分共存，并且不处于快速相互转化平衡。通过透析从盐酸胍中回收蛋白质，恢复了两组分的原始模式。另一方面，在一开始只含有小组分的制剂的盐酸胍溶液中回收的物质中没有发现较大的组分。回收的光谱与起始材料的圆二色性、ph沉淀曲线以及后者被钙离子修饰的方式相似。通过沉降平衡测定分子量表明，4.4-S种的分子量约为230,000，这也是由6 M胍盐酸盐的外推沉降系数得出的值，因此对应于单链（其中两个或多个种在十二烷基硫酸钠存在下在丙烯酰胺凝胶电泳中被溶解）；发现9.7 s物种是二聚体，其特征明显是提取的幽灵蛋白的天然状态。单体和二聚体的摩擦系数有明显差异。二聚体的结构与某种程度上的不对称结构是相容的，但绝不是像肌凝蛋白或副肌凝蛋白一样的分子所期望的程度。
The high-molecular-weight protein component from human erythrocytes has been isolated and its solubility properties studied. In physiological solvent conditions the spectrin is not aggregated and is unaffected, both in hydrodynamic properties and conformation, as judged by circular dichroism and intrinsic fluorescence, by the addition of calcium ions. When the pH is decreased an opalescence first sets in, which corresponds to an associated fibrous state of the protein, and when a critical pH is reached precipitation ensues. The precipitation profile is characterised by extreme sharpness, of the kind observed in the phase separation of polyacid-polybase mixtures or of polyampholytes. The addition of calcium ions displaces this precipitation edge towards higher pH. Sodium ions have a similar but smaller effect. The position of the profile is significantly displaced in aged spectrin preparations, or those from frozen erythrocyte ghosts. Fresh preparations of spectrin consist predominantly of a component sedimenting at 9.7 S, with a minor component at 4.4 S (and traces of higher aggregates). The pattern is independent of the ionic strength, or of the presence or absence of calcium ions. The proportion of the small component increases with time, and in spectrin preparations from frozen ghosts it invariably predominates. At low concentrations of guanidine hydrochloride the larger component gives place progressively to the smaller, and vanishes completely when the concentration of the denaturant reaches 1 M. The two components coexist at concentrations below this, and are not in rapid interconversion equilibrium. On recovery of the protein from the guanidine hydrochloride by dialysis, the original pattern of two components is regained. On the other hand the larger component is not found in the material recovered from guanidine hydrochloride solutions of preparations that contain only the small component at the outset. The recovered spectrin is similar to the starting material in its circular dichroism, in its pH-precipitation profiles, and the manner in which the latter is modified by calcium ions. Molecular weight determination by sedimentation equilibrium shows that the 4.4-S species has a molecular weight of some 230 000, which is also the value derived from the extrapolated sedimentation coeffiecient in 6 M guanidine hydrochloride, and thus corresponds to single chains (of which two or more species are resolved in acrylamide gel electrophoresis in the presence of sodium dodecylsulphate); the 9.7-S species, which characterises what is evidently the native state of the extracted spectrin, is found to be a dimer. The frictional coefficients of the monomer and dimer are appreciably different. That of the dimer is compatible with a somewhat asymmetric structure, but by no means to the extent expected for a myosin-like or paramyosin-like molecule.