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Combined use of freeze‐fracture electron microscopy and X‐ray diffraction for the structure determination of three‐dimensionally ordered specimens
Author(s) -
GulikKrzywicki Thaddée,
Delacroix Hervé
Publication year - 1994
Publication title -
biology of the cell
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 85
eISSN - 1768-322X
pISSN - 0248-4900
DOI - 10.1111/j.1768-322x.1994.tb00930.x
Subject(s) - electron microscope , diffraction , fracture (geology) , crystallography , cryofixation , resolution (logic) , electron diffraction , electron density , materials science , microscopy , electron , symmetry (geometry) , x ray crystallography , x ray , scanning electron microscope , molecular physics , physics , optics , geometry , chemistry , mathematics , composite material , quantum mechanics , artificial intelligence , computer science
The cubic phases of lipid‐water systems have been studied by freeze‐fracture electron microscopy. The preservation of the sample structure following cryofixation was verified by low temperature X‐ray diffraction. Different types of fracture planes were identified; all display highly ordered two‐dimensional domains, each subdivided into sub‐domains related to each other by displacements and rotations related to the symmetry of the space group. The images were filtered using cross‐correlation averaging techniques and the filtered images were compared to the corresponding planar sections of the electron density maps. Several conclusions were drawn: 1) when properly cryofixed, as assessed by low temperature X‐ray diffraction, the structure of the sample was well preserved in the replicas; 2) the symmetry of the space group was faithfully reflected in the electron microscope images; 3) the crystallographic orientations of the most frequently identified'fracture planes coincided with those of the most intense X‐ray reflections indicating that the fracture propagates, preferentially, in regions where the electron density variations are the largest; 4) when different structural models are compatible with X‐ray diffraction data, it is possible to determine the correct model by comparing the filtered images with sections of the corresponding electron density maps; and 5) this approach constitutes a new and powerful tool of general interest for the low resolution study of three‐dimensionally ordered specimens.