Anisotropy in sickle hemoglobin fibers from variations in bending and twist.
Anisotropy in sickle hemoglobin fibers from variations in bending and twist.
复制标题
镰状血红蛋白纤维因弯曲和扭曲的变化而产生各向异性。
DOI：
10.1016/j.jmb.2006.01.071
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
Josephs,R
中科院分区：
文献类型：
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作者：
Turner,MS;Briehl,RW;Wang,JC;Ferrone,FA;Josephs,R
本文研究了镰状血红蛋白纤维的扭转和弯曲的变化。我们发现，这些变化是一致的平衡热波动的起源，这使我们能够估计弯曲和扭转刚度和有效的相应的材料模量。我们通过冷冻水合纤维的电子显微镜测量弯曲，并发现弯曲持续长度，即由于热波动而开始显著弯曲之前所需的纤维长度，为130 μ m，比以前使用光学显微镜报道的要短一些。通过重新分析以前发表的实验结果，发现扭转持续长度仅为2.5 μ m。引人注目的是，这意味着纤维的相应扭转刚度仅为6 × 10 − 27 Jm，远低于其弯曲刚度5 × 10 − 25 Jm。对于（正常的）各向同性材料，人们反而会期望它们是相似的。因此，我们提出了第一个定量的证据，一个非常显着的材料各向异性在镰状血红蛋白纤维，可能会出现从轴向和横向接触之间的差异纤维。我们认为，相对于扭曲变形的纤维的相对柔软度有助于HbS纤维的亚稳性：HbS双股在纤维中被扭曲，但不是在平衡结晶状态。我们的测量告知纤维的热力学稳定性的理论模型，该模型考虑了纤维内血红蛋白（双）链的弯曲和延伸/压缩。
We have studied the variations of twist and bend in sickle hemoglobin fibers. We find that these variations are consistent with an origin in equilibrium thermal fluctuations, which allows us to estimate the bending and torsional rigidities and effective corresponding material moduli. We measure bending by electron microscopy of frozen hydrated fibers and find that the bending persistence length, a measure of the length of fiber required before it starts to be significantly bent due to thermal fluctuations, is 130μm, somewhat shorter than that previously reported using light microscopy. The torsional persistence length, obtained by re-analysis of previously published experiments, is found to be only 2.5μm. Strikingly this means that the corresponding torsional rigidity of the fibers is only 6×10−27Jm, much less than their bending rigidity of 5×10−25Jm. For (normal) isotropic materials, one would instead expect these to be similar. Thus, we present the first quantitative evidence of a very significant material anisotropy in sickle hemoglobin fibers, as might arise from the difference between axial and lateral contacts within the fiber. We suggest that the relative softness of the fiber with respect to twist deformation contributes to the metastability of HbS fibers: HbS double strands are twisted in the fiber but not in the equilibrium crystalline state. Our measurements inform a theoretical model of the thermodynamic stability of fibers that takes account of both bending and extension/compression of hemoglobin (double) strands within the fiber.