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International
Tables for Crystallography Volume B Reciprocal space Edited by U. Shmueli © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. B. ch. 2.2, pp. 233-234
Section 2.2.10.4.2. The SIRAS, MIRAS and MAD cases
aDipartimento Geomineralogico, Campus Universitario, I-70125 Bari, Italy |
Isomorphous replacement and anomalous scattering are discussed in Chapter 2.4![[link]](/graphics/greenarr.gif)
and in IT F
(2001). We observe here only that the SIRAS case can lead algebraically to unambiguous phase determination provided the experimental data are sufficiently good. Thus, any probabilistic treatment must take into consideration errors in the measurements.
In the MIRAS and MAD cases the system is overconditioned: again any probabilistic treatment must consider errors in the measurements, but now overconditioning allows the reduction of the perverse effects of the experimental errors and (in MIRAS) of the lack of isomorphism.
A particular application of extreme relevance concerns the location of anomalous scatterers when selenomethionine-substituted proteins and MAD data are available (Hendrickson & Ogata, 1997; Smith, 1998). In this case, many selenium sites should be identified and usual Patterson-interpretation methods can be expected to fail. The successes of SnB and HB prove the essential role of direct methods in this important area.
References
International Tables for Crystallography
(2001). Vol. F. Macromolecular crystallography, edited by M. G. Rossmann & E. Arnold. Dordrecht: Kluwer Academic Publishers.Google Scholar
Hendrickson, W. A. & Ogata, C. M. (1997). Phase determination from multiwavelength anomalous diffraction measurements. Methods Enzymol. 276, 494–523.Google Scholar
Smith, J. L. (1998). Multiwavelength anomalous diffraction in macromolecular crystallography. In Direct methods for solving macromolecular structures, edited by S. Fortier, pp. 221–225. Dordrecht: Kluwer Academic Publishers.Google Scholar
