THE POTENTIAL AND LIMITATIONS OF NEUTRONS, ELECTRONS AND X-RAYS FOR ATOMIC-RESOLUTION MICROSCOPY OF UNSTAINED BIOLOGICAL MOLECULES
THE POTENTIAL AND LIMITATIONS OF NEUTRONS, ELECTRONS AND X-RAYS FOR ATOMIC-RESOLUTION MICROSCOPY OF UNSTAINED BIOLOGICAL MOLECULES
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DOI：
10.1017/s003358350000305x
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发表时间：
1995-05-01
影响因子：
6.1
通讯作者：
HENDERSON, R
中科院分区：
文献类型：
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作者：
HENDERSON, R
辐射损伤是阻止使用任何种类的显微镜以原子分辨率确定单个生物大分子结构的主要问题。无论使用中子、电子还是X射线作为照明，都是如此。对于中子，核俘获截面和相关的能量沉积和辐射损伤可以通过使用被狂暴氘化和N-15标记的样品以及通过使用快中子来减少，但是单分子生物显微镜仍然是不可行的。对于天然存在的生物材料，电子目前提供了给定量的辐射损伤的最多信息。使用相差电子显微镜对生物分子和类似于10（5）分子量及以上的大分子组装体进行分析，理论上图像中存在足够的信息以允许确定单个颗粒的位置和取向：然后可以使用平均方法的应用来提供原子分辨率结构。需要大约10000个颗粒的图像。低于10（5）分子量，需要某种晶体或其它几何有序聚集体来提供足够高的组合分子量以允许配向。在实践中，最佳图像的当前质量仍然低于理论上可达到的质量，这意味着必须平均更多数量的颗粒，并且分子量限制略大于预测的限制。福尔斯。对于X射线，每个有用的弹性散射事件的损伤量是所有波长和能量的电子的几百倍，因此对样品尺寸和颗粒数量的要求相应地更大。由于在可预见的未来缺乏足够明亮的中子源，电子显微镜在实践中提供了最大的潜力，立即取得进展。
Radiation damage is the main problem which prevents the determination of the structure of a single biological macromolecule at atomic resolution using any kind of microscopy. This is true whether neutrons, electrons or X-rays are used as the illumination. For neutrons, the cross-section for nuclear capture and the associated energy deposition and radiation damage could be reduced by using samples that are fury deuterated and N-15-labelled and by using fast neutrons, but single molecule biological microscopy is still not feasible. For naturally occurring biological material, electrons at present provide the most information for a given amount of radiation damage. Using phase contrast electron microscopy on biological molecules and macromolecular assemblies of similar to 10(5) molecular weight and above, there is in theory enough information present in the image to allow determination of the position and orientation of individual particles: the application of averaging methods can then be used to provide an atomic resolution structure. The images of approximately 10000 particles are required. Below 10(5) molecular weight, some kind of crystal or other geometrically ordered aggregate is necessary to provide a sufficiently high combined molecular weight to allow for the alignment. In practice, the present quality of the best images still falls short of that attainable in theory and this means that a greater number of particles must be averaged and that the molecular weight limitation is somewhat larger than the predicted limit. For X-rays, the amount of damage per useful elastic scattering event is several hundred times greater than for electrons at all wavelengths and energies and therefore the requirements on specimen size and number of particles are correspondingly larger. Because of the lack of sufficiently bright neutron sources in the foreseeable future, electron microscopy in practice provides the greatest potential for immediate progress.