Molecular Cloning and Characterization of <small>L</small>-Galactose-1-phosphate Phosphatase from Tobacco (<i>Nicotiana tabacum</i>)

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  • SAKAMOTO Shingo
    Graduate School of Biosphere Sciences, Hiroshima University Graduate School of Biosphere Sciences, Hiroshima University
  • FUJIKAWA Yukichi
    Graduate School of Biosphere Sciences, Hiroshima University Graduate School of Biosphere Sciences, Hiroshima University
  • TANAKA Nobukazu
    Center for Gene Science, Hiroshima University Center for Gene Science, Hiroshima University
  • ESAKA Muneharu
    Graduate School of Biosphere Sciences, Hiroshima University Graduate School of Biosphere Sciences, Hiroshima University

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  • Molecular Cloning and Characterization of L-Galactose-1-phosphate Phosphatase from Tobacco (Nicotiana tabacum)

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Abstract

L-Galactose-1-phosphate phosphatase (GPPase) is an enzyme involved in ascorbate biosynthesis in higher plants. We isolated a cDNA encoding GPPase from tobacco, and named it NtGPPase. The putative amino acid sequence of NtGPPase contained inositol monophosphatase motifs and metal binding sites. Recombinant NtGPPase hydrolyzed not only L-galactose-1-phosphate, but also myo-inositol-1-phosphate. The optimum pH for the GPPase activity of NtGPPase was 7.5. Its enzyme activity required Mg2+, and was inhibited by Li+ and Ca2+. Its fluorescence, fused with green fluorescence protein in onion cells and protoplasts of tobacco BY-2 cells, was observed in both the cytosol and nucleus. The expression of NtGPPase mRNA and protein was clearly correlated with L-ascorbic acid (AsA) contents of BY-2 cells during culture. The AsA contents of NtGPPase over expression lines were higher than those of empty lines at 13 d after subculture. This suggests that NtGPPase contributes slightly to AsA biosynthesis.

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