Electron Diffraction with the Transmission Electron Microscope as a Phase-Determining Diffractometer-From Spatial Frequency Filtering to the Three-Dimensional Structure Analysis of Ribosomes

Chemists recognize X‐ray crystal structure analysis and electron microscopy as powerful methods of analysis. In the last 20 years the basic ideas of X‐ray diffraction analysis have been extended to the field of electron microscopy, whereby an image‐forming apparatus is converted into an electron diffractometer, and through which an old dream of crystallographers can be realized—the measurement of the phase shift of scattered waves, a prerequisite for the direct calculation of structures. Its most important area of application, like that of the X‐ray diffractometer, is in three‐dimensional structure analysis—in all fields of science. However, beyond crystallography, aperiodic structures (comparable to crystals with a single unit cell) can also be analyzed three‐dimensionally. In this progress report, the development of the first idea (spatial frequency filtering) to the analysis of ribosomal particles is outlined. Attention will be focused primarily on quantitative methods for the measurement of scattered rays, which are also usable beyond the conventional limit of resolution, down to atomic resolution. In the course of this work in 1968, the principle of the three‐dimensional analysis of native biological crystal structures using the electron microscope, as worked with today in many laboratories, was developed. In Munich, however, further research focused on the three‐dimensional analysis of aperiodic and individual (especially biological) objects. The analysis of 50S‐subunits of the procaryotic ribosome of E. coli showed surprisingly good reproducibility of the results (although only within the same orientation), allowing the deduction of almost ideal average model structures from a limited number of particles.