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. 18.5, p. 411
Section 18.5.7.1. Full-matrix comparison with the diffraction-component precision index
a
Chemistry Department, UMIST, Manchester M60 1QD, England |
The DPI (18.5.6.9) with R was offered as a quick and rough guide for the diffraction-data-only error for an atom with . The necessary data for the comparison with the two unrestrained full-matrix inversions of Section 18.5.5 are given in Table 18.5.7.1. For concanavalin A with , the full-matrix quadratic (18.5.4.2b) gives 0.033 Å for a carbon atom and the DPI gives 0.034 Å for an unspecified atom. For the immunoglobulin with , the full-matrix quadratic (18.5.4.2a) gives for a carbon atom, while the DPI gives 0.22 Å.
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For these two structures, the simple DPI formula compares surprisingly well with the unrestrained full-matrix calculations at .
For the restrained full-matrix calculations on concanavalin A, the quadratic (18.5.4.2c) with gives for a carbon atom, which is only 15% smaller than the unrestrained 0.033 Å. This small decrease matches the discussion of and in Section 18.5.4.1 following equation (18.5.4.1). But that discussion also indicates that for the immunoglobulin, the restrained , which was not computed, will be proportionaly much lower than the unrestrained value of , since the restraints are relatively more important in the immunoglobulin.