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Multiwavelength anomalous diffraction
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
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
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
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
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
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
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
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
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 ...
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
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
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
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
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
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
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
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
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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