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Yamamoto K Miyake H Kusunoki M Osaki S 《Journal of Bioscience and Bioengineering》2011,112(6):545-550
The structures of the E277A isomaltase mutant from Saccharomyces cerevisiae in complex with isomaltose or maltose were determined at resolutions of 1.80 and 1.40 Å, respectively. The root mean square deviations between the corresponding main-chain atoms of free isomaltase and the E277Α-isomaltose complex structures and those of free isomaltase and the E277A-maltose complex structures were found to be 0.131 Å and 0.083 Å, respectively. Thus, the amino acid substitution and ligand binding do not affect the overall structure of isomaltase. In the E277A-isomaltose structure, the bound isomaltose was readily identified by electron densities in the active site pocket; however, the reducing end of maltose was not observed in the E277A-maltose structure. The superposition of maltose onto the E277A-maltose structure revealed that the reducing end of maltose cannot bind to the subsite + 1 due to the steric hindrance from Val216 and Gln279. The amino acid sequence comparisons with α-glucosidases showed that a bulky hydrophobic amino acid residue is conserved at the position of Val216 in α-1,6-glucosidic linkage hydrolyzing enzymes. Similarly, a bulky amino acid residue is conserved at the position of Gln279 in α-1,6-glucosidic linkage-only hydrolyzing α-glucosidases. Ala, Gly, or Asn residues were located at the position of α-1,4-glucosidic linkage hydrolyzing α-glucosidases. Two isomaltase mutant enzymes – V216T and Q279A – hydrolyzed maltose. Thus, the amino acid residues at these positions may be largely responsible for determining the substrate specificity of α-glucosidases. 相似文献
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Transparent Nano-Composites Ceramics by Annealing of Amorphous Phase in the HfO2 -Al2 O3 -GdAlO3 System
Shunji Araki Masahiro Yoshimura 《International Journal of Applied Ceramic Technology》2004,1(2):155-160
We have succeeded in fabricating transparent nano-structured ceramics by annealing of the amorphous phase obtained by the solidification of the eutectic melt in the ternary system HfO2 − Al2 O3 − GdAlO3 . The ceramics annealed at 1273 K for 6 hr contained 5-10-nm cubic hafnia grains, and those annealed at 1273 K for 72 hr contained both cubic hafnia and gadolinium aluminum garnet grains 5-10 nm in size. They showed high transparency. Annealing at 1473 K, however, resulted in grain growths that brought about non-transparency. 相似文献
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This paper considers the optimal spare ordering policies for a cold standby redundant system with two dissimilar units. Especially, the planned maintenance schedule with salvage cost is discussed. The failure time distributions for respective units are assumed to be arbitrary. By applying the expected cost per unit time in the steady-state and the stationary availability as criteria of optimality, the optimal ordering policy minimizing or maximizing each criterion is obtained under some economical and/or physical assumptions. Finally, numerical examples are presented, and the effect of the failure time distributions for the optimal ordering policy is examined in detail. 相似文献
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Evaporation behavior of water/solvent blends was estimated using the universal functional activity coefficient, UNIFAC, method. The evaporation rate from a free surface of a waterborne coating, WBC, containing a co-solvent was experimentally determined. These results were used to estimate the evaporation rate from wet films of a WBC containing a variety of co-solvents with a range of initial thickness. Knowing the composition of the WBC during the drying process, the change in the viscosity and the surface tension was determined. The results strongly support the development of a surface tension gradient in the film. It is also suggested that a surface tension gradient would accelerate the leveling of the ribs if a proper co-solvent were employed. 相似文献
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A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter. 相似文献