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Isomorphous replacement (IR) is historically the most common approach to solving the phase problem in X-ray crystallography studies of proteins.For protein crystals this method is conducted by soaking the crystal of a sample to be analyzed with a heavy atom solution or co-crystallization with the heavy atom.
The Patterson function is used to solve the phase problem in X-ray crystallography. It was introduced in 1935 by Arthur Lindo Patterson while he was a visiting researcher in the laboratory of Bertram Eugene Warren at MIT. [1] [2] The Patterson function is defined as
In physics, the phase problem is the problem of loss of information concerning the phase that can occur when making a physical measurement. The name comes from the field of X-ray crystallography , where the phase problem has to be solved for the determination of a structure from diffraction data. [ 1 ]
Molecular replacement (MR) [1] is a method of solving the phase problem in X-ray crystallography.MR relies upon the existence of a previously solved protein structure which is similar to our unknown structure from which the diffraction data is derived.
Anomalous X-ray scattering (MAD or SAD phasing) – the X-ray wavelength may be scanned past an absorption edge [a] of an atom, which changes the scattering in a known way. By recording full sets of reflections at three different wavelengths (far below, far above and in the middle of the absorption edge) one can solve for the substructure of ...
Single-wavelength anomalous diffraction (SAD) is a technique used in X-ray crystallography that facilitates the determination of the structure of proteins or other biological macromolecules by allowing the solution of the phase problem.
Multi-wavelength anomalous diffraction (sometimes Multi-wavelength anomalous dispersion; abbreviated MAD) is a technique used in X-ray crystallography that facilitates the determination of the three-dimensional structure of biological macromolecules (e.g. DNA, drug receptors) via solution of the phase problem.
The sial has a lower density (2700–2800 kg/m 3 [7]) than the sima, which is primarily due to increased amounts of aluminium, and decreased amounts of iron and magnesium. The base of the sial is not a strict boundary, the sial grades into the denser rocks of the sima.