Volume 09（2004）
（財）高輝度光科学研究センター 副理事長、放射光研究所長 Director General of Synchrotron Radiation Research Laboratory, Vice President of JASRI
1. SPring-8の現状／PRESENT STATUS OF SPring-8
Report of the Proposal Review Committee on the 14th Public Research Term 2004B
東京工業大学 応用セラミックス研究所 Materials and Structures Laboratory, Tokyo Institute of Technology
東京工業大学 応用セラミックス研究所 Materials and Structures Laboratory, Tokyo Institute of Technology
2. ビームライン／BEAMLINES
[1]（独）理化学研究所 播磨研究所、理学電機株式会社 Ｘ線研究所 Harima Institute, RIKEN / X-ray Research Laboratory, Rigaku Corporation、[2]（独）理化学研究所 播磨研究所 Harima Institute, RIKEN
（財）高輝度光科学研究センター、大阪大学名誉教授 JASRI / Professor Emeritus, Osaka University
愛媛大学 地球深部ダイナミクス研究センター Geodynamics Research Center, Ehime University
- Abstract
- Carbonates are important constituents of marine sediments and play an important role in the long-term recycling of carbon in the Earth’s deep interior via subduction of oceanic plates. We studied the stability of magnesite, the major carbonate in the mantle, by in situ X-ray diffraction measurements using a combination of laser-heated diamond anvil cell (LHDAC) and synchrotron radiation at BL10XU. We found that magnesite is stable at pressure up to ~115 GPa, at temperatures of ~ 2100 - 2200K, whereas it transforms to a new phase at higher pressures. The diffraction data of the new phase, magnesiteⅡ, are reasonably indexed on the basis of an orthorhombic system, yielding a density of 5.2 g/cm3 at 119 GPa, at room temperature. The present results suggest that magnesite and its high-pressure form are the major hosts for carbon throughout the most parts of the Earth’s lower mantle.
[1]（財）高輝度光科学研究センター 利用研究促進部門Ⅰ Materials Science Division, JASRI、[2]日本原子力研究所 中性子利用研究センター Neutron Science Research Center, Japan Atomic Energy Research Institute、[3]東京理科大学 基礎工学部 Faculty of Industrial Science and Technology, Tokyo University of Science
- Abstract
- Inorganic glasses normally exhibit a network of interconnected covalent-bonded structural elements that has no long-range order. In silicate glasses the network formers are based on SiO4-tetrahedra of which the interconnectivity is realized by sharing the oxygen atoms at the corners. Conventional wisdom then implies that alkaline and alkaline-earth orthosilicate materials cannot be vitrified because they do not contain sufficient network forming SiO2 to establish the needed interconnectivity. We have studied a bulk magnesium orthosilicate glass obtained by levitation melting- and-cooling. We find that the role of network former is largely taken on by corner- and edge-sharing ionic magnesium species that adopt 4-, 5- and 6-coordination with oxygen.
京都大学 工学研究科 Graduate School of Engineering, Kyoto University
[1]名古屋大学 遺伝子実験施設 Center for Gene Research, Nagoya University、[2]京都大学大学院 薬学研究科 Graduate School of Pharmaceutical Sciences, Kyoto University、[3]京都大学大学院 薬学研究科 Graduate School of Pharmaceutical Sciences, Kyoto University、[4]名古屋大学 遺伝子実験施設 Center for Gene Research, Nagoya University
- Abstract
- KaiA, KaiB, and KaiC constitute the circadian clock machinery in cyanobacteria. KaiA activates kaiBC expression while KaiC represses it. Here we demonstrated that KaiA is composed of three functional domains : the N-terminal amplitude-amplifier domain, the central period-adjuster domain, and the C-terminal clock-oscillator domain. The C-terminal domain is responsible for dimer formation, binding to KaiC, enhancing KaiC phosphorylation, and generating circadian oscillations. The 1.8 Å X-ray crystal structure of the C-terminal clock-oscillator domain of KaiA from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 shows that residue His270, located at the center of a KaiA dimer concavity, is essential to KaiA function. KaiA binding to KaiC likely occurs via the concave surface. Based on the structure, we could predict the structural roles of the residues that affected circadian oscillations.
3. 最近の研究から／FROM LATEST RESEARCH
京都大学大学院 生命科学研究科／（独）理化学研究所 播磨研究所 Graduate School of Biostudies, Kyoto University / Harima Institute, RIKEN
- Abstract
- Photosynthesis is a multi-step reaction that utilizes light energy to convert carbon dioxide into sugar and generate oxygen as by-product. The first step of photosynthesis is the oxygen-evolving reaction performed by the protein-pigment complex called “photosystem II”, and PsbP is one of the protein subunits constituting photosystem II. Since PsbP exists only in higher plants and green algae, its existence has been the subject of inquiry in the process of plant evolution. In order to elucidate the origin and function of PsbP from its 3D structure, a high-resolution analysis based on multiple wavelength anomalous dispersion method using the X-ray of SPring-8 was conducted. The result showed that the structure of PsbP was not similar to any known structures in photosystem II from cyanobacteria, primitive organisms doing oxygenic photosynthesis. This research shows one aspect of the evolution of oxygenic photosynthetic organisms.
名古屋大学 工学研究科 Department of Applied Physics, Nagoya University
- Abstract
- The precise crystal structure of Zn4Sb3, which is one of the most efficient thermoelectric materials, has been determined by combination of Maximum Entropy Method and Rietveld analysis using synchrotron-radiation powder diffraction at SPring-8. The structure contains significant disorder with zinc atoms distributed over multiple positions. The crystal structure of Zn4Sb3 in present study allows a general explanation of the electric transport properties which explains the remarkable thermoelectric figure of merit.
研究成果報告会 プログラム委員会 Program Committee, Meeting on the Results of Research Activities
兵庫県立大学大学院 物質理学研究科 Graduate School of Material Science, University of Hyogo
広島大学大学院 工学研究科 Graduate School of Engineering, Hiroshima University
[1]理化学研究所 播磨研究所 Harima Institute, RIKEN、[2]京都大学 大学院理学研究科 Graduate School of Science, Kyoto University
- Abstract
- Five Lol proteins are involved in the lipoprotein transport in Gram-negative bacteria. Crystal structures of a lipoprotein-specific periplasmic chaperone, LolA, and an outer membrane lipoprotein receptor, LolB from Escherichia coli were determined using diffraction data collected at the beamlines of SPring-8. Despite their dissimilar amino acid sequences (identity ~ 8%), the structures of LolA and LolB are strikingly similar to each other. Both have a hydrophobic cavity consisting of an unclosed β-barrel and an α-helical lid. The cavity represents a possible binding site for the lipid moiety of lipoproteins. However, the structural differences in size and shape of hydrophobic inner spaces between LolA and LolB are highly connected to the functional differences between two proteins. Furthermore, these structural differences between two proteins provide significant insights into the molecular mechanisms underlying the energy-independent transfer of lipoproteins from LolA to LolB, and from LolB to the outer membrane.
[1]大阪大学 蛋白質研究所 Institute for Protein Research, Osaka University、[2]京都大学大学院 工学研究科 Graduate School of Engineering, Kyoto University、[3]（独）理化学研究所 播磨研究所 Harima Institute, RIKEN
- Abstract
- The compaction process in protein folding has not been characterized well due to experimental difficulties. The submillisecond-resolved observation system for small-angle X-ray scattering was developed and applied for the process of apomyoglobin folding. It was demonstrated that the secondary and tertiary structures are largely organized cooperatively; however, the initial folding phase involves a significant collapse of their main chain structures. A common folding mechanism was proposed, in which hydrophobic environments realized by the initial collapse prompts the subsequent formation of helical structures.
兵庫県立大学大学院 生命理学研究科 Graduate School of Life Science, University of Hyogo
- Abstract
- Improved X-ray structures of bovine heart cytochrome c oxidase (at 1.8/1.9 Å resolution in the fully oxidized/reduced states) show that the net positive charge created upon oxidation of the low-spin heme of the enzyme (heme a) drives the active proton transport from the interior of the mitochondria to Asp51 across the enzyme via a water channel and a hydrogen-bond network, located in tandem, and that the enzyme reduction induces proton ejection from the aspartate to the mitochondrial exterior. A peptide bond in the hydrogen-bond network critically inhibits reverse proton transfer through the network. A redox-coupled change in the capacity of the water channel, induced by the hydroxyfarnesylethyl group of heme a, suggests that the channel functions as an effective proton collecting region. The Asp51Asn mutation of the bovine enzyme abolishes its proton-pumping function without impairment of the dioxygen reduction activity. Infrared results indicate that the conformation of Asp51 is controlled only by the oxidation state of heme a. These results indicate that heme a drives the proton pumping process.
前兵庫県警察本部 科学捜査研究所長 Former Director, Forensic Science Laboratory, Hyogo Prefectural Police Headquarters
大阪大学 蛋白質研究所 Institute for Protein Research, Osaka University
- Abstract
- The photosynthetic unit of oxygenic photosynthesis is organized as two large multimolecular membrane complexes, photosystem II (PSII) and photosystem I (PSI). The two photosystems operate in series linked by a third multiprotein complex called the cytochrome b6f complex. The cytochrome b6f complex is a membrane-spanning protein complex embedded in a thylakoide membrane of photosynthetic organisms. The b6f complex arranges the electron transfer between plastoquinol reduced by PSII and an electron carrier protein plastocyanin that connects to PSI. The structure of the b6f complex from cyanobacterium M. laminosus was solved at 3.0 Å resolution by isomorphous replacement method and multiwavelength anomalous diffraction from native iron atoms. The crystal structures of the cytochrome b6f complex complete the description of the architecture of the oxygenic photosynthetic electron transport chain, since three-dimensional structures have been provided for two photosystems.
[1]日本原子力研究所 関西研究所 放射光科学研究センター Synchrotron Radiation Research Center, Kansai Research Establishment, JAERI、[2]スプリングエイトサービス㈱ SPring-8 Service Co., Ltd
- Abstract
- The decomposition and melting behaviors of GaN under high pressures and temperatures were studied by in situ x-ray diffraction experiments using a large volume multi-anvil high-pressure apparatus at beamline BL14B1. GaN decomposed into Ga melt and N2 at lower pressures than 5.5 GPa. At pressures above 6.0 GPa, however, congruent melting of GaN occurred around 2220 ℃, and decreasing the temperature allowed the GaN melt to crystallize to the original structure. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions. The present results have great potential in providing high quality bulk single crystals of GaN, which are desirable substrates for fabricating optoelectronic devices.
[1]大阪市立大学大学院 理学研究科 Graduate School of Science, Osaka City University、[2]慶應義塾大学 理工学部 Faculty of Science and Technology, Keio University、[3]名古屋大学大学院 工学研究科 Graduate School of Engineering, Nagoya University、[4]広島大学大学院 工学研究科 Graduate School of Engineering, Hiroshima University
- Abstract
- VIth group elements like C, Si, Ge and Sn make clusters consisting of pentagonal and/or hexagonal plolyhedra. A avarious crystals having hierachical structure can be constructed on a basis of these clusters. Recent strong demand from the field of isotope engineering for semiconductors has spurred on efforts that have led to the successful separation of stable Si isotopes. The combination of nano clusters and pure isotopes may open a new field of materials science. The present paper describnes, as such examples, the clarification of superconducting mechanism of the first discovered silicon-network Si46 superconductor. An approach of all silicon quantum computors using 28Si isotope is also demonstrated.
（独）理化学研究所 播磨研究所 研究推進部 Research Promotion Division, Harima Institute, RIKEN
4. 研究会等報告／WORKSHOP AND COMMITTEE REPORT
日本原子力研究所 関西研究所 放射光科学研究センター Synchrotron Radiation Research Center, Kansai Research Establishment, JAERI
[1]高エネルギー加速器研究機構 物質構造科学研究所 Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK)、[2]（財）高輝度光科学研究センター 利用研究促進部門Ⅰ Materials Science Division, JASRI
（財）高輝度光科学研究センター 利用研究促進部門Ⅱ Life and Environmental Science Division, JASRI
（財）高輝度光科学研究センター 総務部 Personnel Section General Affairs Division, JASRI
（独）理化学研究所 播磨研究所 新竹電子ビーム光学研究室 RIKEN Harima Institute, Advanced Electron Beam Physics Laboratory
5. 談話室・ユーザー便り／OPEN HOUSE･A LETTERS FROM SPring-8 USERS
SPring-8利用者懇談会 会長 名古屋大学大学院 工学研究科 Graduate School of Engineering, Nagoya University
