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Multiwavelength anomalous diffraction
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, ch. 14.2, pp. 373-378 [ doi:10.1107/97809553602060000845 ]
... scattering effects measured at several X-ray wavelengths can provide a direct solution to the crystallographic phase problem. For many years this was appreciated as a hypothetical possibility (Okaya & Pepinsky, 1956), but, until tunable synchrotron radiation ... experiment (Hoppe & Jakubowski, 1975). Multiwavelength anomalous diffraction (MAD) became a dominant phasing method in macromolecular crystallography with the advent ...

Determination of the anomalous-scatterer partial structure
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, Section 14.2.7, p. 377 [ doi:10.1107/97809553602060000845 ]
... structure Determination of the partial structure of anomalous scatterers is a prerequisite for MAD-phased electron density, regardless of the phasing ... larger differences or . The approximation is accurate for only a small fraction of reflections because there is little correlation between and . However, it suffices for a suitably strong signal and a suitably small number of ...

Approaches to MAD phasing
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, Section 14.2.6, pp. 376-377 [ doi:10.1107/97809553602060000845 ]
... the explicit approach, the MAD observational equation is solved directly (Hendrickson et al., 1988; Hendrickson & Ogata, 1997). In the pseudo-MIR approach, MAD phasing is treated as a special case of multiple isomorphous replacement (Burling et al., ...

Data handling
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, Section 14.2.5, p. 376 [ doi:10.1107/97809553602060000845 ]
... equalizing systematic errors is known as `phase first, merge later' (Hendrickson, 1985; Hendrickson & Ogata, 1997). The idea is that systematic errors may ... be amplified by merging data, and that this may obscure a weak phasing signal. In this approach, the individual observations ...

Experimental considerations
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, Section 14.2.4, pp. 375-376 [ doi:10.1107/97809553602060000845 ]
Experimental considerations 14.2.4. Experimental considerations The design and execution of a MAD experiment are distinguished from monochromatic experiments in macromolecular crystallography ... avoid complications from other edges or to obtain data at a wavelength optimal for model refinement. In the case of anomalous ... absorption edge from the labelled macromolecule at the time of a MAD experiment. Even when the position of the edge ...

Diffraction ratios for estimating the MAD phasing signal
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, Section 14.2.3, p. 375 [ doi:10.1107/97809553602060000845 ]
... the MAD phasing signal The first consideration in design of a MAD experiment is the choice of anomalous scatterer(s) with ... scattering of biological macromolecules:Note: the estimated total scattering of a protein is coincidentally . The diffraction ratios relevant to a MAD experiment with N anomalous-scatterer sites are for ...

A phase equation for MAD
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, Section 14.2.2, pp. 374-375 [ doi:10.1107/97809553602060000845 ]
A phase equation for MAD 14.2.2. A phase equation for MAD The impact of anomalous scattering on ... structure-factor expression according to wavelength dependence (Karle, 1980). A wavelength-independent structure factor with phase is defined to ...

Anomalous scattering factors
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, Section 14.2.1, pp. 373-374 [ doi:10.1107/97809553602060000845 ]
... stimulation. The magnitude of is normalized to the scattering by a single electron. Thus the `normal' scattering factor is a real number, equal to the Fourier transform of the electron ... model of atomic scattering is known as anomalous scattering. Using a classical mechanical model (James, 1948), an atom scatters as ...

General anomalous-scatterer labels for biological macromolecules
Smith, J. L. and Hendrickson, W. A.  International Tables for Crystallography (2012). Vol. F, Section 14.2.8, pp. 377-378 [ doi:10.1107/97809553602060000845 ]
... 14.2.8. General anomalous-scatterer labels for biological macromolecules MAD requires a suitable anomalous scatterer, of which none are generally present in ... SeMet) substituted for the natural amino acid methionine (Met) is a general anomalous-scattering label for proteins (Hendrickson, 1985), and is the anomalous scatterer most frequently used ...

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