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1.
Murakami K Irie K Ohigashi H Hara H Nagao M Shimizu T Shirasawa T 《Journal of the American Chemical Society》2005,127(43):15168-15174
Amyloid fibrils mainly consist of 40-mer and 42-mer peptides (Abeta40, Abeta42). Abeta42 is believed to play a crucial role in the pathogenesis of Alzheimer's disease because its aggregative ability and neurotoxicity are considerably greater than those of Abeta40. The neurotoxicity of Abeta peptides involving the generation of free radicals is closely related to the S-oxidized radical cation of Met-35. However, the cation's origin and mechanism of stabilization remain unclear. Recently, structural models of fibrillar Abeta42 and Abeta40 based on systematic proline replacement have been proposed by our group [Morimoto, A.; et al. J. Biol. Chem. 2004, 279, 52781] and Wetzel's group [Williams, A. D.; et al. J. Mol. Biol. 2004, 335, 833], respectively. A major difference between these models is that our model of Abeta42 has a C-terminal beta-sheet region. Our biophysical study on Abeta42 using electron spin resonance (ESR) suggests that the S-oxidized radical cation of Met-35 could be generated by the reduction of the tyrosyl radical at Tyr-10 through a turn structure at positions 22 and 23, and stabilized by a C-terminal carboxylate anion through an intramolecular beta-sheet at positions 35-37 and 40-42 to form a C-terminal core that would lead to aggregation. A time-course analysis of the generation of radicals using ESR suggests that stabilization of the radicals by aggregation might be a main reason for the long-lasting oxidative stress of Abeta42. In contrast, the S-oxidized radical cation of Abeta40 is too short-lived to induce potent neurotoxicity because no such stabilization of radicals occurs in Abeta40. 相似文献
2.
Serber Z Straub W Corsini L Nomura AM Shimba N Craik CS Ortiz de Montellano P Dötsch V 《Journal of the American Chemical Society》2004,126(22):7119-7125
Studying protein components of large intracellular complexes by in-cell NMR has so far been impossible because the backbone resonances are unobservable due to their slow tumbling rates. We describe a methodology that overcomes this difficulty through selective labeling of methyl groups, which possess more favorable relaxation behavior. Comparison of different in-cell labeling schemes with three different proteins, calmodulin, NmerA, and FKBP, shows that selective labeling with [(13)C]methyl groups on methionine and alanine provides excellent sensitivity with low background levels at very low costs. 相似文献
3.
4.
Fumiaki Ishii Toshio Ohga Akihiro Tsutsumi Hiroji Ohigashi 《Journal of Polymer Science.Polymer Physics》2002,40(10):1026-1037
The heterogeneous higher order structure and molecular motion in a single crystalline film of a vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer with 73 mol % VDF was investigated with the 1H–13C cross‐polarization/magic‐angle spinning NMR technique. A transient oscillation was observed in plots of the 13C peak intensity versus the contact time for the CH2, CHF, and CF2 groups. On the basis of the extended cross‐relaxation theory of spin diffusion, we determined that the oscillation behavior was caused by the TrFE‐rich segments in the chain and that the crystal consisted of VDF‐rich and TrFE‐rich domains. The former had TrFE‐rich segments in VDF and TrFE fractions of 0.24 and 0.27, respectively, and the latter had VDF‐rich segments in a VDF fraction of 0.49. The spin–lattice relaxation time T1ρH in the rotating frame for each group was minimal in the three temperature regions of β, αb, and αc (↑) on heating and in the two temperature regions of α1D and αc (↓) on cooling. The αc (↑) and αc (↓) processes depended on the first‐order ferroelectric phase‐transition regions on heating and cooling, respectively. The motional modes for the other processes were confirmed by the T1ρH minimum behavior of the VDF and TrFE groups in the TrFE‐rich domain and the VDF‐rich segments in the VDF‐rich domain. The β and αb processes were attributed to the flip–flop motion of the TrFE‐rich segments and the competitive motion of the TrFE‐ and VDF‐rich segments in the ferroelectric phase, respectively. The α1D process was due to the one‐dimensional diffusion motion of the conformational defects along the chain in the paraelectric phase, accompanied by the trans and gauche transformation of the VDF conformers of ttg+tg? and g+tg?tt. The effect of the competitive motion of the TrFE‐rich segment on the thermal stability of the VDF‐rich segment in the chain near the Curie temperature was examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1026–1037, 2002 相似文献
5.
Wang H Jeong HY Imura M Wang L Radhakrishnan L Fujita N Castle T Terasaki O Yamauchi Y 《Journal of the American Chemical Society》2011,133(37):14526-14529
Here we report a novel hard-templating strategy for the synthesis of mesoporous monocrystalline Pt nanoparticles (NPs) with uniform shapes and sizes. Mesoporous Pt NPs were successfully prepared through controlled chemical reduction using ascorbic acid by employing 3D bicontinuous mesoporous silica (KIT-6) and 2D mesoporous silica (SBA-15) as a hard template. The particle size could be controlled by changing the reduction time. Interestingly, the Pt replicas prepared from KIT-6 showed polyhedral morphology. The single crystallinity of the Pt fcc structure coherently extended over the whole particle. 相似文献
6.
A wide variety of transducer shapes and applications exists in the field of diagnostic ultrasound. As a basic material ferro-electric ceramics are used almost exclusively, but polymer piezoelectric material seems a new alternative. By comparing in a qualitative way the most relevant parameters of these materials, a state of the art judgement may be made about their applicability in diagnostic ultrasound. 相似文献
7.
Yoshiaki Tsunawaki Nobuhisa Ohigashi Kunioki Mima Shin-ichiro Kurama Kazuo Imasaki Masayuki Fujita Chiyoe Yamanaka Sadao Nakai 《International Journal of Infrared and Millimeter Waves》1995,16(1):317-325
A three dimensional simulation software system developed to estimate a free electron laser (FEL) gain has been applied to FEL using a standard plane polarized wiggler and an alternately shifted magnet wiggler. It is seen for the latter wiggler that a large filling factor could be selected and each maximum gain corresponding to each orbit of electron beam concentrates at a certain frequency region of FEL radiation. It is, therefore, implied that a proper shift between the adjacent magnets in the wiggler produces the improvement of the FEL gain. 相似文献
8.
9.
Yoshiaki Tsunawaki Mie Noguchi Mitsuhiro Kusaba Nobuhisa Ohigashi Masayuki Fujita Kazuo Imasaki Shin-ichiro Kuruma Kunioki Mima Sadao Nakai Chiyoe Yamanaka 《International Journal of Infrared and Millimeter Waves》1998,19(2):177-184
A hybrid planar wiggler with a period of 20 mm has been studied as the simplest one which gives the strong field including some higher harmonic components by selecting proper sizes of the ferromagnetic and the permanent magnet. Small gap length of the wiggler and small width of permendur satisfy these conditions to a certain degree.Gain analysis of FEL suggests that for high wiggler field of K>1 1.6, higher harmonic gains are improved primarily due to its strong field, and for low wiggler field of K< 1 1.6, they are mainly due to the modification of the wiggler field distribution. 相似文献
10.
Fukuta Y Mita T Fukuda N Kanai M Shibasaki M 《Journal of the American Chemical Society》2006,128(19):6312-6313
An asymmetric ring-opening reaction of meso-aziridines with TMSN3 was developed using a catalyst prepared from Y(OiPr)3 and chiral ligand 2 in a 1:2 ratio. Excellent enantioselectivity was realized from a wide range of substrates with a practical catalyst loading. The products were efficiently converted to enantiomerically enriched 1,2-diamines, which are versatile chiral building blocks for pharmaceuticals and chiral ligands. This reaction was applied to a catalytic asymmetric synthesis of Tamiflu, a very important anti-influenza drug containing a chiral 1,2-diamino functionality. 相似文献