Decoration and shadowing of freeze-etched catalase crystals.
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 180 K. 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 on 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.
L
L
Bachmann
R
R
Becker
G
G
Leupold
M
M
Barth
R
R
Guckenberger
W
W
Baumeister
D000818:Animals; D002374:Catalase / Q000032:analysis*; D002417:Cattle; D003460:Crystallization; D005613:Freeze Etching / Q000379:methods; D006046:Gold; D008854:Microscopy, Electron / Q000379:methods; D010984:Platinum; D011487:Protein Conformation; D013194:Staining and Labeling; D014961:X-Ray Diffraction
D010984:Platinum; D006046:Gold; D002374:Catalase