Briehl R W, Mann E S, Josephs R
Department of Physiology & Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461.
J Mol Biol. 1990 Feb 20;211(4):693-8. doi: 10.1016/0022-2836(90)90070-3.
Electron microscopy of sickle cell hemoglobin fibers fixed at different times during gelation shows an exponential distribution of fiber lengths, with many short fibers and few long ones. The distribution does not change significantly with time as polymerization progresses. If this distribution of lengths reflects kinetic mechanism of fiber assembly, it complements information from studies of the progress of average properties of the polymers and, as has been done for other rod-like polymerizing systems, permits testing of models for the mechanism of fiber assembly. In this case, the results are consistent with the double nucleation model of Ferrone et al. or with a related alternative model based on fiber breakage. However, other possible causes of this microheterogeneity exist, including: breakage due to solution shearing of the long, rod-like, fibers; the presence of residual nuclei; equilibrium relations governing polymerization; and breakage of solid-like but weak gels that develop early and adhere to the grid. The arguments against the first three of these possibilities suggest that they are not responsible. However, breakage of entanglements or cross-links in a solid-like and adherent gel is consistent with the distributions.
对凝胶化过程中不同时间点固定的镰状细胞血红蛋白纤维进行电子显微镜观察，结果显示纤维长度呈指数分布，短纤维多，长纤维少。随着聚合反应的进行，这种分布不会随时间发生显著变化。如果这种长度分布反映了纤维组装的动力学机制，那么它补充了聚合物平均性质研究的信息，并且如同对其他棒状聚合体系所做的那样，允许对纤维组装机制的模型进行检验。在这种情况下，结果与费罗内等人的双成核模型或基于纤维断裂的相关替代模型一致。然而，这种微观异质性还存在其他可能原因，包括：长棒状纤维因溶液剪切而断裂；残留核的存在；控制聚合反应的平衡关系；以及早期形成并附着在网格上的类固体但较弱凝胶的断裂。对前三种可能性的反驳表明它们并非原因所在。然而，类固体且附着的凝胶中缠结或交联的断裂与分布情况相符。
