Multiple-wavelength anomalous diffraction

A teclmique that employs principles similar to those of isomorphous replacement is multiple-wavelength anomalous diffraction (MAD) [27]. The expression for the atomic scattering factor in equation (B1.8.2h) is strictly accurate only if the x-ray wavelength is well away from any characteristic absorption edge of the element, in which case the atomic scattering factor is real and Filiki) = Fthkl V- Since the diffracted... 

Ealick, S.E. (2000) Advances in multiple wavelength anomalous diffraction crystallography, Curr. Opin. Chem. Biol., 4, 495-499. 

The multiple-wavelength anomalous diffraction method (MAD) relies upon sufficiently strong anomalously scattering atoms in the protein structure itself In this method, diffraction data must be collected at a number of different wavelengths, usually requiring data collection with... 

From a relatively small begiiming, nearly two decades ago (Guss et al., 1988 Murthy et al., 1988 Hendrickson et al., 1988, 1989), phase calculation using Multiple-wavelength Anomalous Diffraction (MAD) data has become more widespread and generally used. There are many reviews that cover diverse aspects of the process (Hendrickson, 1991 Smith, 1991 Ogata, 1998 Ealick, 2000). This review will concentrate on the most recent developments and experimental details, and is essentially an update to the author s earlier review (Krishna Murthy, 1996). 

Krishna Murthy H. M. (1996). The use of multiple wavelength anomalous diffraction in ab initio phase determination. Method Mol. Biol. 56,127-152. 

Alternative methods of solving the phase problem are also used now. When a transition metal such as Fe, Co, or Ni is present in the protein, anomolous scattering of X-rays at several wavelengths (from synchrotron radiation) can be used to obtain phases. Many protein structures have been obtained using this multiple wavelength anomalous diffraction (MAD phasing) method.404 407 408 Selenocysteine is often incorporated into a protein that may be produced in... 

MWPCs have been successfully used at LURE and Stanford for multiple wavelength anomalous dispersion phasing measurements (see chapter 9). An MWPC has also been used to record Laue diffraction patterns at VEPP-3 (Gaponov et al 1989a,b,c). 

The intensity differences obtained in the diffraction pattern by illuminating such a crystal by x-rays of different wavelengths can be used in a way similar to the method of multiple isomorphous replacement to obtain the phases of the diffracted beams. This method of phase determination which is called Multiwavelength Anomalous Diffraction, MAD, and which was pioneered by Wayne Hendrickson at Columbia University, US, is now increasingly used by protein cystallographers. 

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