Comparison of slam-freezing and high-pressure freezing effects on the DNA cholesteric liquid crystalline structure
Comparison of slam-freezing and high-pressure freezing effects on the DNA cholesteric liquid crystalline structure
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DOI：
10.1046/j.1365-2818.1996.1090666.x
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发表时间：
1996-10-01
影响因子：
2
通讯作者：
Dubochet, J
中科院分区：
文献类型：
--
作者：
Leforestier, A;Richter, K;Dubochet, J
使用超薄冷冻水合切片和冷冻断裂复制品的并行电子显微镜，我们比较了两种冷冻技术的超微结构后果：液氦温度下的猛烈冷冻和高压冷冻，在模型系统上，DNA胆甾型液晶相。这两种冷冻技术都能使含水量高达 85% 的 DNA 液晶溶液玻璃化，但会引起分子组织的结构重排。尽管机械压应力引起周期性变形，但通过坝冻结方法保留了胆甾结构。相比之下，高压冷冻不会保留液晶的结构：长程胆甾分层消失，并且分子之间的焦点连续扭曲被修改。这些结果表明，玻璃化虽然是必要的，但可能不足以保存水合材料的天然状态。我们讨论了由于高压冷冻过程允许的低冷冻速率而在样本中发生的分子重排的可能起源。
Using in parallel electron microscopy of ultrathin frozen-hydrated sections and freeze-fracture replicas, we compare the ultrastructural consequences of two freezing techniques: slam-freezing at liquid helium temperature and high-pressure freezing, on a model system, the DNA cholesteric liquid crystalline phase. Both freezing techniques are able to vitrify DNA liquid crystalline solutions containing up to 85% water, but induce structural rearrangements of the molecular organization. The cholesteric structure is preserved by the dam-freezing method despite the formation of periodic distortions induced by the mechanical compressive stress. In contrast, high-pressure freezing does not preserve the structure of the liquid crystal: the long-range cholesteric stratification disappears, and the focal continuous twist between molecules is modified. These results show that vitrification, though necessary, may not be a sufficient token of preservation of the native state of hydrated materials, We discuss the possible origins of the molecular rearrangements that have time to occur in the specimens as a result of the low freezing rate permitted by the high-pressure freezing process.