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71.
Fujita Izumi; Komeiji Yuto; Yamato Ichiro 《Protein engineering, design & selection : PEDS》1995,8(9):935-938
A mutational study was performed on the corepressor (Ltryptophan)binding site of the trp repressor of Escherichia coli. Threonine81, one of the residues forming the hydrophobic pocket of thebinding site, was replaced with Ser, Cys and Met by cassettemutagenesis. Biochemical characterization showed that all thesemutations caused a moderate decrease in tryptophan binding activity(free energy change 1 kcal/mol). The results suggested thatthe binding pocket is rather flexible in the vicinity of Thr81.On the other hand, the mutations produced a discernible decreasein the repressor activity in vivo, apparently by weakening oreliminating the hydrogen bond between Thr81 and the operatorDNA, as well as by introducing possible side-chain rearrangement. 相似文献
72.
Akira Kishimoto Yuto TakagawaTakashi Teranishi Hidetaka Hayashi 《Materials Letters》2011,65(14):2197-2200
Alumina/carbon-black composite ceramics with different percolation thresholds were fabricated by changing the size ratio of constituent particles. The dependence of resistivity on pressure was established for each sample. The compositional dependence of resistivity can be explained by percolation theory. The percolation threshold decreases with increasing alumina/carbon-black particle size ratio. The pressure dependence of the resistivity increases as the composition approaches the percolation threshold. When the relative composition at the percolation threshold is fixed, the sensitivity increases with increasing matrix/dispersoid initial particle size ratio. 相似文献
73.
Yusuke Shiratori Teppei Ogura Hironori Nakajima Mio Sakamoto Yutaro Takahashi Yuto Wakita Takuya Kitaoka Kazunari Sasaki 《International Journal of Hydrogen Energy》2013
Inorganic fiber network including YSZ fiber which acts as catalyst support was created by the simple paper-making process, and novel Ni-loaded paper-structured catalysts (PSCs) with excellent catalytic activity for the dry reforming of methane were designed and developed. The PSCs exhibited high fuel conversion comparable to the conventional powdered catalysts with less than one-tenth catalyst weights. The significant advantages of the PSCs are their high mechanical flexibility and material workability. So far, a functionally-graded catalytic reaction field which leads to uniform temperature distribution during biogas reforming resulting in stable operation of planar SOFC was successfully developed by the PSC array based on the kinetic simulation model built in this research. 相似文献
74.
Tatsushi Saito Yuto Ishikawa Yusuke Noda Tatsuya Yokoi Yu Oshima Atsutomo Nakamura Katsuyuki Matsunaga 《Journal of the American Ceramic Society》2023,106(2):1587-1596
First-principles calculations were performed to reveal an effect of Ca vacancies on the stability of substitutional divalent cations M2+ (M = Mg, Zn, Sr) in Ca-deficient hydroxyapatite (dHAp). M2+ concentrations up to 20 mol% in dHAp were considered, and the most stable substitutional sites and their lowest energy configurations in the dHAp lattice were examined with the aid of a generic algorithm method. It was found that defect formation energies of substitutional M2+ are lower in dHAp than in stoichiometric HAp (sHAp) at all M2+ concentrations. This indicates that these M2+ ions are more favorably involved in dHAp than in sHAp, which is in reasonable agreement with experiment. Detailed analyses on atomic structures in dHAp show that the presence of a Ca vacancy varies its surrounding Ca–O bond lengths over a wide area so that Ca–O polyhedrons with various sizes are produced. As a result, M2+ ions can predominantly occupy Ca sites at which M2+ fits better, depending on the ionic radii of M2+. For Zn2+ substitution in dHAp, its defect formation energy decreases more with the increasing concentrations and has the minimum value at 15 mol%. Such a trend can be understood from changes in effective coordination numbers of Zn in dHAp. 相似文献
75.
Sangho Koh Masahiro Mizuno Yuto Izuoka Naoto Fujino Naoko Hamada-Sato Yoshihiko Amano 《Journal of Applied Glycoscience》2021,68(1):11
The genus Pestalotiopsis are endophytic fungi that have recently been identified as cellulolytic system producers. We herein cloned a gene coding for a xylanase belonging to glycoside hydrolase (GH) family 10 (PesXyn10A) from Pestalotiopsis sp. AN-7, which was isolated from the soil of a mangrove forest. This protein was heterologously expressed by Pichia pastoris as a host, and its enzymatic properties were characterized. PesXyn10A was produced as a glycosylated protein and coincident to theoretical molecular weight (35.3 kDa) after deglycosylation by peptide-NfF-glycosidase F. Purified recombinant PesXyn10A exhibited maximal activity at pH 6.0 and 50 °C, and activity was maintained at 90 % at pH 5.0 and temperatures lower than 30 °C for 24 h. The substrate specificity of PesXyn10A was limited and it hydrolyzed glucuronoxylan and arabinoxylan, but not β-glucan. The final hydrolysis products from birchwood xylan were xylose, xylobiose, and 1,23-α-D-(4-O-methyl-glucuronyl)-1,4-β-D-xylotriose. The addition of metallic salts (NaCl, KCl, MgCl2, and CaCl2) activated PesXyn10A for xylan degradation, and maximal activation by these divalent cations was approximately 160 % at a concentration of 5 mM. The thermostability of PesXyn10A significantly increased in the presence of 50 mM NaCl or 5 mM MgCl2. The present results suggest that the presence of metallic salts at a low concentration, similar to brackish water, exerts positive effects on the enzyme activity and thermal stability of PesXyn10A. 相似文献