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Biological specimen preparation; Electron microscope examination of materials; Molecular biophysics; Proteins; Interactions with radiations at the biomolecular level [A8715M]; Biophysical instrumentation and techniques [A8780]
Abstract:
Aqueous suspensions of catalase crystals were freeze-cleaved, deep-etched and either shadowed with Ta/W at 45 degrees or decorated with 0.1-0.9 nm thick deposits of Au and Pt at normal incidence. The electron micrographs of the decorated specimens were processed by correlation averaging and compared with a relief reconstruction obtained from shadowed specimens. Pronounced decoration was observed on the catalase crystals at temperatures between 130 and 180K. Disregarding the difficulties in interpretation, the averages of 0.1-0.2 nm thick Au and Pt films reveal more structural detail than the relief reconstruction. Perfect shadowing provides information of surface topography and is relatively easy to comprehend; decoration renders variations in physico-chemical affinity visible. Problems of the interference of decoration and shadowing effects in the intuitive interpretation of freeze-etch replicas and in relief reconstruction are discussed as well as the disturbing effects of a non-ideal carbon backing. The perspectives of using decoration intentionally as a positive staining technique for the investigation of frozen-hydrated surfaces are evaluated and quality criteria are defined. (29 References).
