PubMed · 9671285
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P Campbell. 1998-07-09. New policy for structure data.. https://doi.org/10.1038/27971
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New algorithms have been outlined for efficient calculation of the fast Fourier transform of data revealing crystallographic symmetries in previous papers by Rowicka, Kudlicki & Otwinowski [Acta Cryst. (2002), A58, 574-579; Acta Cryst. (2003), A59, 172-182; Acta Cryst. (2003), A59, 183-192]. The present paper deals with three implementation-related issues, which have not been discussed before. First, the shape of the FFT-asymmetric unit in the reciprocal space is discussed in detail. Next, a method is presented of reducing symmetry in-place, without the need to allocate memory for intermediate results. Finally, there is a discussion on how the algorithm can be used for the inverse Fourier transform. The results are derived for the case of the one-step symmetry reduction [Rowicka, Kudlicki & Otwinowski (2003). Acta Cryst. A59, 172-182]. The algorithms are also an important step in the more complicated cases of centered lattices [Rowicka, Kudlicki & Otwinowski (2003). Acta Cryst. A59, 183-192] and space groups with non-removable special positions, such as cubic groups [Rowicka, Kudlicki & Otwinowski (2004), in preparation]. In the present paper, as in our previous ones, complex-to-complex FFTs only are dealt with. Modifications needed to adapt the results to data with Hermitian symmetry will be described in our forthcoming article [Kudlicki, Rowicka & Otwinowski (2004), in preparation].
Compound refractive lenses (CRLs) are effective for collimating or focusing high-energy X-ray beams (50-100 keV) and can be used in conjunction with crystal optics in a variety of configurations, as demonstrated at the 1-ID undulator beamline of the Advanced Photon Source. As a primary example, this article describes the quadrupling of the output flux when a collimating CRL, composed of cylindrical holes in aluminium, is inserted between two successive monochromators, i.e. a modest-energy-resolution premonochromator followed by a high-resolution monochromator. The premonochromator is a cryogenically cooled divergence-preserving bent double-Laue Si(111) crystal device delivering an energy width DeltaE/E approximately 10(-3), which is sufficient for most experiments. The high-resolution monochromator is a four-reflection flat Si(111) crystal system resembling two channel-cuts in a dispersive arrangement, reducing the bandwidth to less than 10(-4), as required for some applications. Tests with 67 and 81 keV photon energies show that the high-resolution monochromator, having a narrow angular acceptance of a few microradians, exhibits a fourfold throughput enhancement due to the insertion of a CRL that reduces the premonochromatized beam's vertical divergence from 29 micro rad to a few microradians. The ability to focus high-energy X-rays with CRLs having long focal lengths (tens of meters) is also shown by creating a line focus of 70-90 micro m beam height in the beamline end-station with both the modest-energy-resolution and the high-energy-resolution monochromatic X-rays.
Cytochrome c peroxidase was isolated from Paracoccus denitrificans and purified to homogeneity in three steps prior to crystallization. Two different diffraction-quality crystal forms were obtained by the hanging-drop vapour-diffusion method using a number of screening conditions. The best (needle-shaped) crystal form is suitable for structural studies and was grown from solutions containing 20% PEG 8000, 0.1 M Tris pH 8.5 and 0.2 M MgCl(2). Crystals grew to a maximum length of approximately 0.7 mm and belong to the primitive monoclinic space group P2(1), with unit-cell parameters a = 78.3, b = 51.0, c = 167.2 A, beta = 97.9 degrees. After a dehydration step and extensive optimization of the cryocooling conditions, a complete data set was collected to 2.2 A from a native crystal of the fully oxidized form of the enzyme using synchrotron radiation.