The catalytic architecture of leukotriene C4 synthase with two arginine residues.

Leukotriene (LT) C(4) and its metabolites, LTD(4) and LTE(4), are involved in the pathobiology of bronchial asthma. LTC(4) synthase is the nuclear membrane-embedded enzyme responsible for LTC(4) biosynthesis, catalyzing the conjugation of two substrates that have considerably different water solubility; that amphipathic LTA(4) as a derivative of arachidonic acid and a water-soluble glutathione (GSH). A previous crystal structure revealed important details of GSH binding and implied a GSH activating function for Arg-104. In addition, Arg-31 was also proposed to participate in the catalysis based on the putative LTA(4) binding model. In this study enzymatic assay with mutant enzymes demonstrates that Arg-104 is required for the binding and activation of GSH and that Arg-31 is needed for catalysis probably by activating the epoxide group of LTA(4).

X-ray absorption fine structure combined with x-ray fluorescence spectrometry. Part 15. Monitoring of vanadium site transformations on titania and in mesoporous titania by selective detection of the vanadium K alpha1 fluorescence.

X-ray absorption fine structure combined with X-ray fluorescence spectrometry was applied to various V+TiO2 hybrid samples. Emitted V K alpha1 fluorescence from the sample was selectively counted by using a high-energy-resolution (0.4 eV) spectrometer equipped with a Ge(331) crystal. Two advantages of this method, extremely high signal/background ratio and the compatibility of measurements in the atmosphere of reaction gas (in situ study in relation to heterogeneous catalysis), were effective at the V K-edge. Structure transformation of the V sites was spectroscopically followed for the V/TiO2 catalyst. The monooxo tetrahedral vanadate site was demonstrated to exist at 473 K. It transformed into dispersed species of 5-fold coordination in ambient air and further into polymeric VO(x) species in 0.85 kPa of water at 290 K. In the presence of 3.2 kPa of 2-propanol, dissociative adsorption of 2-propanol on the dispersed V species was strongly suggested at 290-473 K. In situ structure changes of V sites on TiO2 were reported by means of XAFS for the first time. The V(V) sites for the V/TiO2 catalysts were essentially identical with those for V supported on mesoporous (high-surface-area) TiO2 and V-TiO2 sample prepared by the sol-gel method. However, predominant V(IV) sites were found for mesoporous V-TiO2. The V(IV) sites substituted on the Ti sites of TiO2. When the molar ratio of V/Ti increased from 1/100 to 1/5.0, major octahedral V sites in the TiO2 matrix looked to transform into tetrahedral ones.

High-resolution and high-intensity powder diffractometer at BL15XU in SPring-8.

A new ultra-high-resolution powder diffractometer for synchrotron radiation has been constructed at beamline BL15XU, SPring-8. The two-axis diffractometer is optimized for high-flux and high-coherent X-ray beams, which are provided by combining a planar undulator and a large offset rotated-inclined Si(111) double-crystal monochromator. The optics design of the diffractometer is based on transmission geometry, which employs a capillary specimen and reflection geometries using a flat-plate specimen. The intensity data are collected using a 2theta step-scan technique in both geometries. The diffractometer can be arranged in a variety of optical configurations, e.g. simple receiving slits, flat crystal analyzer of Ge(111) or Si(111), and in-vacuum-type long horizontal parallel slits. A minimum full width at half-maximum against 2theta was 0.00572 degrees at lambda = 0.63582 A for the (200) reflections from Si powder in the transmission geometry employing the Ge(111) crystal analyzer. A wide temperature range (32-900 K), which is controlled by a He/N(2) gas stream system, is available. 288 structure parameters of a zeolite ZSM-5 sample have been demonstrated to successfully refine with a R(wp) value of 6.96% by a Rietveld analysis of the high-resolution powder diffraction data from a 1 mm-diameter capillary specimen.

Non-existence of positive glitches in spectra using the YB(66) double-crystal monochromator of BL15XU at Spring-8.

YB(66) is suitable for dispersing synchrotron radiation in the 1-2 keV energy range with a 2d lattice spacing of 1.17 nm. When used with an undulator there are no positive glitches at 1385.6 and 1438 eV in spectra dispersed by a YB(66) 400 double-crystal monochromator as observed using bending-magnet or wiggler beamlines. The transmission function of a YB(66) double-crystal monochromator has been measured by means of a Si PIN photodetector, and X-ray absorption near-edge structure (XANES) of Mg, Al and Si were measured at high resolution. From all of these experiments it has been clarified that a YB(66) double-crystal monochromator is well suited for soft X-ray beamlines on third-generation light sources.