Multiwavelength Anomalous Diffraction method

La Fortelle, E. D. and Bricogne, G. (1997). Maximum-likelihood heavy-atom parameter refinement for multiple isomorphous replacement and multiwavelength anomalous diffraction methods. Method Enzymol. 276, 472 94. 

Kinetic analysis gave Km values of 67 pM for formaldehyde and 56 pM for NAD+, and suggested that the reaction proceeds by a ping-pong mechanism. The enzyme catalyzed the oxidation of formaldehyde accompanied by the stoichiometric reduction of NAD", but no reverse reaction was observed. The crystal structure of FaidDH from Pseudomonas putida (PFDH) has been solved by the multiwavelength anomalous diffraction method using intrinsic zinc ions and has been refined at a 1.65 A resolution (Fig. 9.3) [87]. 

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. 

Ramakrishnan, V. and Biou, V. (1997). Treatment of multiwavelength anomalous diffraction data as a special case of multiple isomorphous replacement. Method Enzymol. 276, 538-557. 

The tem ARO/CYC crystal structure was solved to 1.9 A using the multiwavelength anomalous diffraction (MAD) method. Our model reveals the following conclusions ... 

X-ray crystallography is a widely used teclmique for the three-dimensional structure analysis of RNA molecules. The extraction of information from X-ray diffraction patterns from RNA crystals requires proper phase determinations using methods such as multiwavelength anomalous dispersion in which placement of specific heavy atoms is required. Seleiuum-modi-fled ribonucleotides have been used for these purposes by Du et al. (36), because the selenium atom does not seem... 

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