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31.
Schick M Xie X Ataka K Kahnt J Linne U Shima S 《Journal of the American Chemical Society》2012,134(6):3271-3280
[Fe]-hydrogenase catalyzes the reversible hydride transfer from H(2) to methenyltetrahydromethanoptherin, which is an intermediate in methane formation from H(2) and CO(2) in methanogenic archaea. The enzyme harbors a unique active site iron-guanylylpyridinol (FeGP) cofactor, in which a low-spin Fe(II) is coordinated by a pyridinol-N, an acyl group, two carbon monoxide, and the sulfur of the enzyme's cysteine. Here, we studied the biosynthesis of the FeGP cofactor by following the incorporation of (13)C and (2)H from labeled precursors into the cofactor in growing methanogenic archaea and by subsequent NMR, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) and IR analysis of the isolated cofactor and reference compounds. The pyridinol moiety of the cofactor was found to be synthesized from three C-1 of acetate, two C-2 of acetate, two C-1 of pyruvate, one carbon from the methyl group of l-methionine, and one carbon directly from CO(2). The metabolic origin of the two CO-ligands was CO(2) rather than C-1 or C-2 of acetate or pyruvate excluding that the two CO are derived from dehydroglycine as has previously been shown for the CO-ligands in [FeFe]-hydrogenases. A formation of CO from CO(2) via direct reduction catalyzed by a nickel-dependent CO dehydrogenase or from formate could also be excluded. When the cells were grown in the presence of (13)CO, the two CO-ligands and the acyl group became (13)C-labeled, indicating either that free CO is an intermediate in their synthesis or that free CO can exchange with these iron-bound ligands. Based on these findings, we propose pathways for how the FeGP cofactor might be synthesized. 相似文献
32.
Co/-Al2O3 catalysts prepared at different calcination temperatures were tried in methane reforming with CO2 and characterized by XRD, H2-TPR and coking reaction via CH4 temperature-programmed decomposition. Characterizations indicated that the surface species of Co, reforming activity and coke formation rate strongly depended on calcination temperature and reduction time.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
33.
Gangfeng Huang Dr. Tristan Wagner Dr. Ulrich Ermler Dr. Eckhard Bill Dr. Kenichi Ataka Dr. Seigo Shima 《Angewandte Chemie (International ed. in English)》2018,57(18):4917-4920
Mono‐iron hydrogenase ([Fe]‐hydrogenase) reversibly catalyzes the transfer of a hydride ion from H2 to methenyltetrahydromethanopterin (methenyl‐H4MPT+) to form methylene‐H4MPT. Its iron guanylylpyridinol (FeGP) cofactor plays a key role in H2 activation. Evidence is presented for O2 sensitivity of [Fe]‐hydrogenase under turnover conditions in the presence of reducing substrates, methylene‐H4MPT or methenyl‐H4MPT+/H2. Only then, H2O2 is generated, which decomposes the FeGP cofactor; as demonstrated by spectroscopic analyses and the crystal structure of the deactivated enzyme. O2 reduction to H2O2 requires a reductant, which can be a catalytic intermediate transiently formed during the [Fe]‐hydrogenase reaction. The most probable candidate is an iron hydride species; its presence has already been predicted by theoretical studies of the catalytic reaction. The findings support predictions because the same type of reduction reaction is described for ruthenium hydride complexes that hydrogenate polar compounds. 相似文献
34.
35.
Ueda J Ikota N Shinozuka T Yamaguchi T 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(11):2487-2492
The scavenging activity of three fulvic acids (named XWCS-1, XWCS-4, and XWCS-8 according to time taken for ozonolysis) obtained by ozonolysis of humic acid extracted from Xinjiang (China) weathered coal and a fulvic acid (named XWCFA) extracted from the same coal towards reactive oxygen species such as superoxide radical (O(2)(.)(-)) and hydroxyl radical ((.)OH) was investigated with an electron spin resonance (ESR)-spin trapping method using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap. O(2)(.)(-) was generated with a hypoxanthine-xanthine oxidase system. (.)OH was generated by three different methods; (i) FeSO(4)-hydrogen peroxide (H(2)O(2)) system, (ii) Cu(en)(2)-H(2)O(2) system, and (iii) UVB photolysis of H(2)O(2). At physiological pH, XWCS-1 had the greatest O(2)(.)(-) scavenging activity, followed by XWCS-4, XWCS-8 and XWCFA. XWCFA had the greatest ?OH scavenging activity among the four fulvic acids, whereas XWCS-1 and XWCS-4 enhanced the production of (.)OH from a metal-catalyzed hydroxyl radical generating system, suggesting that these molecules act as prooxidants in the presence of metal ion. 相似文献
36.
Designs, Codes and Cryptography - With the development of side-channel attacks, a necessity arises to invent authenticated key exchange protocols in a leakage-resilient manner. Constructing... 相似文献
37.
Shunsuke Yonai Naruhiro Matsufuji Tatsuaki Kanai Yuki Matsui Kaoru Matsushita 《Radiation measurements》2010,45(10):1369-1373
Undesired radiation exposure in normal tissues around a treatment volume in proton and carbon-ion radiotherapies is less than that in the conventional radiotherapies due to physical and/or biological properties of charged particles. Such exposure is always considered in a treatment planning, however, undesired exposure in normal tissues far from the treatment volume cannot be considered in the treatment planning, because it is caused by secondary radiation as well as leakage primary particles. Though this exposure is considerably lower than that near the treatment volume, it may be not negligible to estimate the risk of secondary cancer especially for the young patients. In particular, the assessment of the secondary neutrons that inevitably produced within the patient and beam line devices is very important due to the potency of their biological effect. The distributions of the absorbed dose and the biological effectiveness in phantom/patient are required to assess the risk, and Monte Carlo calculation plays a key role due to a difficulty of the measurements. In this study, comparison of measured and calculated in-air neutrons at the patient position in the Heavy Ion Medical Accelerator in Chiba (HIMAC) treatment room are performed to verify the accuracy of the Monte Carlo code, PHITS. Our calculations underestimated epithermal neutrons measured by Bonner sphere system. This discrepancy may be caused by an insufficiency of the calculational geometry modeling, consequently an underestimation of neutrons scattered and moderated by the beam line devices. However, it is unlikely that the underestimation significantly contribute to the dose estimation in phantom. On the other hand, the calculation reproduced the measured ambient dose equivalents well because they were dominated by neutrons above 0.1 MeV. This result showed that the PHITS code has a potential ability to evaluate the neutron exposure of the patient in passive carbon-ion radiotherapy. 相似文献
38.
39.
This corrigendum provides corrections for several errors in the previously published letter “Heavy-Traffic Asymptotics for Stationary GI/G/1-Type Markov Chains” [Operations Research Letters 40 (2012) 185–189]. 相似文献
40.
Mitsuo Ataka 《Phase Transitions》2013,86(2-3):205-219
There is an increasing need to rationalize protein crystal growth, mostly carried out so far by trial-and-error. The phase rule gives the number of conditions necessary to specify the state of protein crystallization in equilibrium. Unsaturated and supersaturated regions are distinguished in phase diagrams. Examples of such diagrams for protein crystals are tabulated. To determine the phase diagrams reliably, the following items are discussed: (1) proper crystallization methods, (2) the length of time needed for establishing equilibrium, and (3) the importance of specifying the kind of solid state. Various crystallization methods are compared as to their effect on the solution system by using the phase diagrams, and the potential usefulness of the diagrams for crystallizing new proteins is discussed. 相似文献