International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. F. ch. 19.2, p. 423
Section 19.2.3.1. Specimen preparation
aVerna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA |
An electron microscope column is kept at a pressure of < 10−6 Torr (1 Torr = 133.322 Pa). Because a thin protein crystal loses its crystallinity if dried in a vacuum, its hydration can be maintained by embedding it in a thin layer of vitreous ice, glucose, or other small sugar derivatives (Unwin & Henderson, 1975; Dubochet et al., 1988
). The effectiveness of these preservation methods is evidenced by the high-resolution diffraction orders (out to at least 3 Å) from properly embedded protein crystals (Fig. 19.2.3.1)
. Since the high-resolution reflections come mostly from the protein, their diffraction intensities are largely independent of the embedding medium. However, the low-resolution diffraction intensities can be affected by the embedding medium because different media have different scattering densities relative to the protein. For any new crystal, any of the embedding media mentioned above can be used for high-resolution structural studies.
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