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Articles by Xi Liu
Total Records ( 2 ) for Xi Liu
  Mao Ye , Xi Liu and Liyun Zhao
  L-glutaminase could hydrolyze L-glutamine to L-glutamic acid which is an important ‘Umami’ substance. To obtain a salt-tolerant L-glutaminase for application in Chinese soy sauce fermentation, B. amyloliquefaciens Y-9 producing salt-tolerant L-glutaminase was isolated from mangrove sediment. The production of L-glutaminase in Solid State Fermentation (SSF) using agro-industrial residues was optimized using a central composite design of the Response Surface Methodology and the enzyme was purified which was used for further characterization including the optimum and stability of pH and temperature, effect of metal ions, substrate specificity and application to soy sauce fermentation. Under optimized conditions the experimental maximum yield of L-glutaminase reached 19.64±0.63 U gds-1 which is the highest yield obtained in SSF so far. The L-glutaminase was purified to homogeneity with final specific activity of 196.2 U mg-1 protein. The enzyme showed high activity (68% of the original activity) in the presence of 20% NaCl. The enzyme was most stable at pH 5.0 and was highly stable over an acidic pH range (3.0~7.0). These results indicate that this enzyme has a higher salt tolerance and an acidic stability. Furthermore, in Chinese soy sauce fermentation model reaction, the addition of glutaminase from B. amyloliquefaciens Y-9 was highly effective for the production of glutamic acid. This study indicates a possibility to establish economical large-scale production of L-glutaminase and this enzyme is suitable for application in soy sauce liquid fermentation with high-salt process.
  Zi-Liang Wang , Xiao-Peng Xu , Bai-Liang He , Shao-Ping Weng , Jia Xiao , Li Wang , Ting Lin , Xi Liu , Qing Wang , Xiao-Qiang Yu and Jian-Guo He
  Infectious spleen and kidney necrosis virus (ISKNV) causes a pandemic and serious disease in fish. Infection by ISKNV causes epidermal lesions, in which petechial hemorrhages and abdominal edema are prominent features. ISKNV ORF48R contains a domain similar to that of the platelet-derived growth factor and vascular endothelial growth factor (VEGF) families of proteins. ISKNV ORF48R showed higher similarity to the VEGFs encoded by Megalocytivirus and Parapoxvirus than to those encoded in fish and mammals. We used zebrafish as a model and constructed a recombinant plasmid containing the DNA sequence of ISKNV ORF48R to study ISKNV infection. The plasmid was microinjected into zebrafish embryos at the one-cell stage. Overexpression of the ISKNV ORF48R gene results in pericardial edema and dilation at the tail region of zebrafish embryos, suggesting that ISKNV ORF48R induces vascular permeability. ISKNV ORF48R is also able to stimulate a striking expression of flk1 in the zebrafish dorsal aorta and the axial vein. Furthermore, ISKNV ORF48R, while cooperating with zebrafish VEGF121, can stimulate more striking expression of flk1 than can either ISKNV ORF48R or zebrafish VEGF121 alone. However, decreased expression of FLK-1 by gene knockdown results in the disappearance of pericardial edema and dilation at the tail region of zebrafish embryos induced by overexpression of ISKNV ORF48R in the early stages of embryonic development.
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