Dorset D L
Electron Diffraction Department, Hauptman-Woodward Medical Research Institute, Inc., Buffalo, NY 14203-1196, USA.
Proc Natl Acad Sci U S A. 1997 Mar 4;94(5):1791-4. doi: 10.1073/pnas.94.5.1791.
The crystal structure of halorhodopsin is determined directly in its centrosymmetric projection using 6.0-A-resolution electron diffraction intensities, without including any previous phase information from the Fourier transform of electron micrographs. The potential distribution in the projection is assumed a priori to be an assembly of globular densities. By an appropriate dimensional re-scaling, these "globs" are then assumed to be pseudo-atoms for normalization of the observed structure factors. After this treatment, the structure is determined directly by conventional direct methods, followed by Fourier refinement, leading to a mean phase deviation of only 20 degrees (from the values originally found from the image transform) for the 45 most intense reflections.
利用6.0埃分辨率的电子衍射强度，直接在其中心对称投影中确定了嗜盐视紫红质的晶体结构，而不包括来自电子显微镜傅里叶变换的任何先前相位信息。投影中的电位分布先验地假定为球状密度的集合。通过适当的尺寸重新缩放，这些“球”然后被假定为伪原子，用于对观察到的结构因子进行归一化。经过这种处理后，通过传统的直接法直接确定结构，然后进行傅里叶精修，对于45个最强反射，平均相位偏差仅为20度（相对于最初从图像变换中得到的值）。
