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Articles by Li Song
Total Records ( 2 ) for Li Song
  Wang Hu , Haiyan Zhao , Liankun Shan , Li Song , Hui Cao , Zhou Yang , Zihui Cheng , Chunzhu Yan , Sijin Li , Huai Yang and Lin Guo
  A magnetite (Fe3O4) nanoparticle/chiral nematic liquid crystal (N*-LC) composite was prepared and filled into a planar treated cell. The Fe3O4 nanoparticles had been modified by oleic acid so that they could be better dispersed in the composite. When a magnetic field was scanned on the outer surface of the cell locally, Fe3O4 nanoparticles moved towards the inner surface of the cell correspondingly, and the black expected information was displayed. When the magnet was applied to the opposite outer surface, the information was erased. After polymer network walls were prepared in the composite, the resolution of the information displayed increased. Then, through the formation of hydrogen bonds between the nanoparticles and chiral pyridine compound (CPC) doped in the composite, the pitch length of the N*-LC could be adjusted by altering the intensity of the applied magnetic field. The composite doped with CPC could potentially be used as a material for a type of reflective colour paper with magnetically controllable characteristics.
  Lianrui Chu , Yanlai Lai , Xiaoping Xu , Scott Eddy , Shuang Yang , Li Song and David Kolodrubetz
  The metabolism of glutathione by the periodontal pathogen Treponema denticola produces hydrogen sulfide, which may play a role in the host tissue destruction seen in periodontitis. H2S production in this organism has been proposed to occur via a three enzyme pathway, γ-glutamyltransferase, cysteinylglycinase (CGase), and cystalysin. In this study, we describe the purification and characterization of T. denticola CGase. Standard approaches were used to purify a 52-kDa CGase activity from T. denticola, and high pressure liquid chromatography electrospray ionization tandem mass spectrometry analysis of this molecule showed that it matches the amino acid sequence of a predicted 52-kDa protein in the T. denticola genome data base. A recombinant version of this protein was overexpressed in and purified from Escherichia coli and shown to catalyze the hydrolysis of cysteinylglycine (Cys-Gly) with the same kinetics as the native protein. Surprisingly, because sequence homology indicates that this protein is a member of a family of metalloproteases called M17 leucine aminopeptidases, the preferred substrate for the T. denticola protein is Cys-Gly (kcat/Km of 8.2 µM–1 min–1) not L-Leu-p-NA (kcat/Km of 1.1 µM–1 min–1). The activity of CGase for Cys-Gly is optimum at pH 7.3 and is enhanced by Mn2+, Co2+, or Mg2+ but not by Zn2+ or Ca2+. Importantly, in combination with the two other previously purified T. denticola enzymes, γ-glutamyltransferase and cystalysin, CGase mediates the in vitro degradation of glutathione into the expected end products, including H2S. These results prove that T. denticola contains the entire three-step pathway to produce H2S from glutathione, which may be important for pathogenesis.

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