2. D-Xylose and UDP-L-Arabinose in Plants" style="margin:15px;">
    Author's Information
    Toshihisa Kotake
    Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan

    Ryohei Takata
    Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan

    Rajeev Verma
    Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3125, U.S.A.

    Masato Takaba
    Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan

    Daisuke Yamaguchi
    Department of Biochemistry and Molecular Biology, Faculty of Science, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan

    Takahiro Orita
    Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan

    Satoshi Kaneko
    Food Biotechnology Division, National Food Research Institute, 2-1-12, Kannondai, Tsukuba, Ibaraki 305-8642, Japan

    Koji Matsuoka
    Division of Material Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan

    Tetsuo Koyama
    Division of Material Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan

    Wolf-Dieter Reiter
    Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3125, U.S.A.

    Yoichi Tsumuraya
    Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
  3. D-Xylose and UDP-L-Arabinose in Plants" style="margin:15px;">
    Abstract
    UDP-sugars serve as substrates in the synthesis of cell wall polysaccharides and are themselves generated through sequential interconversion reactions from UDP-Glc (UDP-glucose) as the starting substrate in the cytosol and the Golgi apparatus. For the present study, a soluble enzyme with UDP-Xyl (UDP-xylose) 4-epimerase activity was purified approx. 300-fold from pea (Pisum sativum L.) sprouts by conventional chromatography. The N-terminal amino acid sequence of the enzyme revealed that it is encoded by a predicted UDP-Glc 4-epimerase gene, PsUGE1, and is distinct from the UDP-Xyl 4-epimerase localized in the Golgi apparatus. rPsUGE1 (recombinant P. sativum UGE1) expressed in Escherichia coli exhibited both UDP-Xyl 4-epimerase and UDP-Glc 4-epimerase activities with apparent Km values of 0.31, 0.29, 0.16 and 0.15 mM for UDP-Glc, UDP-Gal (UDP-galactose), UDP-Ara (UDP-L-arabinose) and UDP-Xyl respectively. The apparent equilibrium constant for UDP-Ara formation from UDP-Xyl was 0.89, whereas that for UDP-Gal formation from UDP-Glc was 0.24. Phylogenetic analysis revealed that PsUGE1 forms a group with Arabidopsis UDP-Glc 4-epimerases, AtUGE1 and AtUGE3, apart from a group including AtUGE2, AtUGE4 and AtUGE5. Similar to rPsUGE1, recombinant AtUGE1 and AtUGE3 expressed in E. coli showed high UDP-Xyl 4-epimerase activity in addition to their UDP-Glc 4-epimerase activity. Our results suggest that PsUGE1 and its close homologues catalyse the interconversion between UDP-Xyl and UDP-Ara as the last step in the cytosolic de novo pathway for UDP-Ara generation. Alternatively, the net flux of metabolites may be from UDP-Ara to UDP-Xyl as part of the salvage pathway for Ara.
    Keywords
    Arabidopsis, bifunctionality, enzyme kinetics, nucleotide sugar, pea (Pisum sativum), UDP-glucose 4-epimerase (UGE)
    DOI: 10.1042/BJ20091025
    ADLID: 28271-v4
  4. D-Xylose and UDP-L-Arabinose in Plants" style="margin:15px;">
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  1. Keywords
    Arabidopsis bifunctionality enzyme kinetics nucleotide sugar pea (Pisum sativum) UDP-glucose 4-epimerase (UGE)
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