Downing K H
Donner Laboratory, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA.
Scanning Microsc Suppl. 1992;6:43-52.
Three-dimensional structures have recently been determined by electron crystallography at a resolution high enough to determine atomic arrangements in both protein and mineral specimens. The different nature of these two types of specimens produces some very significant differences in the way data is obtained and processed, although the principles are the same. The sensitivity of proteins to damage by the electron beam limits the signal-to-noise ratio in the image and the resolution to which data can be extracted from the image. A number of constraints, such as the amino acid sequence and the connectivity of atoms within amino acids, can be used in interpreting the limited image data. In materials samples, the relative insensitivity to damage allows obtaining resolution limited only by the microscope. In many samples, dynamical scattering and other non-linear effects limit the information in the image, but this limit can be circumvented by working in very thin areas of the specimen.
最近，通过电子晶体学已经确定了三维结构，其分辨率高到足以确定蛋白质和矿物质标本中的原子排列。尽管原理相同，但这两种类型标本的不同性质在数据获取和处理方式上产生了一些非常显著的差异。蛋白质对电子束损伤的敏感性限制了图像中的信噪比以及可从图像中提取数据的分辨率。在解释有限的图像数据时，可以使用一些限制条件，例如氨基酸序列和氨基酸内原子的连接性。在材料样本中，对损伤的相对不敏感性使得能够获得仅受显微镜限制的分辨率。在许多样本中，动态散射和其他非线性效应限制了图像中的信息，但通过在标本的非常薄的区域进行操作可以规避这一限制。
