The growth of multiwavelength anomalous diffraction(MAD) phasing relies on the development of the powerful synchrotron radiation and the freezing of protein crystals to near liquid nitrogen temperatures(100K). The cryocrystallography was developed in the early 1990s. This technology increased the lifetimes of crystals by adding cryoprotectants with harvest solution on the crystals. Then the crystal is mounted under the liquid nitrogen stream to cool the crystal rapidly without damaging it. Because of the reduction in thermal disorder, longer exposure times and a more stable crystal can be obtained and long-term storage and re-used of crystals are also possible. Thus the crystals used in MAD analysis would be reduced and the use of data from a few crystals decreases errors introduced in the scaling and merging of the data sets. Another benefit of the freezing method was the reduction in the demands on the beamline controls and more powerful beamlines can be used. Larger swaths of data could be collected at a single energy without the fear of the loss of diffraction due to radiation damage of the crystal and data collection can be done only in a single crystal.
b.Distribution of the number of structures according to the anomalous scattering element that was used. The Fe, Zn and Cu cluster are proteins that intrinsically contain a usable anomalous scatterer. Sm to U are primarily heavy atom derivatives. The majority of Se and Br structures are from selenomethionyl proteins or brominated bases.
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