Heme oxygenase (HO) plays a central role in heme catabolism, which is involved in keeping iron homeostasis, defense for oxidative stress, and signal transduction in mammals. HO catalyzes the site-specific cleavage of heme to produce biliverdin IXα, CO, and iron using reducing equivalents and O2. To address the reaction mechanism of HO, I determined the crystal structures of rat HO-1 in substrate-free form, heme-bound form, O2-analog bound forms, and biliverdiniron chelate bound form. These structures revealed that the narrow distal pocket of HO limits the direction of distal ligand by which the site-specific cleavage is allowed. Moreover, I discuss how HO incorporates heme and dissociates iron and biliverdin as well. I also determined the crystal structure of rat heme-HO-1 complex in CO bound form and succeeded in trapping an intermediate structure during the CO releasing step. Discrimination mechanism between O2 and CO by HO is discussed based on these structures. Finally I refer to a possibility of development of novel inhibitors to HO using imidazole-dioxolane compounds.
The isolated hydrogen-bonded materials, 5-methyl-9-hydroxyphenalenone (MeHPLN) and 5-bromo-9-hydroxyphenalenone (BrHPLN), were studied by means of X-ray and neutron diffraction methods. It was found that the position of the nucleus of the hydrogen atom in the hydrogen-bond region does not agree with the center of mass of the electron cloud of the hydrogen atom. This leads to a local electronic dipole moment in the hydrogen-bond region. Using the experimentally obtained dipole moment, phase transition temperatures for MeHPLN and BrHPLN were calculated based on a tunneling model. Result shows good agreement with the ones obtained by a dielectric measurement.
Local structures of ion-beam-synthesized amorphous Fe-Si thin layers and their microstructural changes upon thermal annealing have been examined using transmission electron microscopy (TEM) . Atomic pair-distribution functions extracted from electron diffraction patterns revealed that the nature of short-range order in amorphous Fe-Si thin layer can be well described by the atomic arrangements of crystalline iron silicides. The amorphous Fe-Si crystallized into β-FeSi2 after annealing at 1073 K for 2 h, and most of defects were successfully removed. We discussed the recrystallization process of amorphous Fe-Si thin layers as well as the growth mechanism of β-FeSi2 thin layer formed in high-dose Fe ion implanted Si.
Local atomic structures of Pd- and Fe-based metallic glasses were investigated by means of transmission electron microscopy (TEM) . In these typical metallic glasses, local structures of nanoscale phase separation were observed using high-resolution TEM and nanobeam electron diffraction. A structural modeling of the Pd-based metallic glass with the observed local structures was also performed with the help of computer simulation which explained an energy-filtered electron diffraction data. The obtained results show that the comprehensive TEM study is useful to understand nanoscale structural organizations in metallic glasses.
The structures of the melilite (three compounds) have been determined in the range from room temperature up to 773 K. The structures of incommensurate (IC) phase are characterized by bundles of four arrays of the six-coordinated Ca polyhedra with T 1 tetrahedra along the c-axis. The IC phases undergo the phase transition into the normal phases at elevated temperatures. The change of the modulated structure has been clarified by construction of the structures using the desired q-values and the modulation amplitudes determined at 293 K. The change of IC structures is characterized by variable distribution of bundle and octagonal arrangements of them. Large-scale regularities with sizes much larger than the modulation wavelength are also formed in the structures. The structure of commensurate phase of Ca2CoSi2O7 has been determined based on the results of simulation.
New techniques to prepare iodinated derivatives are presented which involve vapor diffusion of iodine and hydrogen peroxide. One of the techniques, termed as Vaporizing Iodine Labeling (VIL) only requires a small amount of KI/I2 droplet to be enclosed into a crystallization well, where iodination of tyrosine residues in target proteins are sometimes occurred. When the iodination is insufficient for phase calculation, a following technique using hydrogen peroxide (HYPER-VIL) further catalyzes the iodination reaction. These techniques are especially useful for phase determination using longer-wavelength X-rays.
The soft X-ray beamline constructed for an industry application is briefly introduced. The varied line spacing plane grating monochromator (VLS-PGM) has been designed in order to cover the wide-energy range from 40-1000 eV with a set of three focusing mirrors and one grating. The resolving power is expected to be more than 5000 with 10 micron slits. The conventional photoelectron spectrometer is installed with an ion gun, a flood gun and a twinanode X-ray source. The instrument for XAFS measurement is also attached to the main chamber.