期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 104, 期 22, 页码 9534-9539出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0701625104
关键词
GDP-L-galactose pyrophosphorylase; gold kiwifruit; VTC2
The gene for one postulated enzyme that converts GDP-L-galactose to L-galactose-1-phosphate is unknown in the L-galactose pathway of ascorbic acid biosynthesis and a possible candidate identified through map-based cloning is the uncharacterized gene At4g26850.We identified a putative function for At4g26850 using PSI-Blast and motif searching to show it was a member of the histidine triad superfamily, which includes D-galactose uridyltransferase. We cloned and expressed this Arabidopsis gene and the homologous gene from Actinidia chinensis in Escherichia coli and assayed the expressed protein for activities related to converting GDP-L-galactose to L-galactose-l-P. The expressed protein is best described as a GDP-L-galactose-hexose-1-phosphate guanyltransferase (EC 2.7.7.), catalyzing the transfer of GMP from GDP-L-galactose to a hexose-l-P, most likely D-mannose-1-phosphate in vivo. Transient expression of this A. chinensis gene in tobacco leaves resulted in a > 31-fold increase in leaf ascorbate as well as a 50-fold increase in GDP-L-galactose-D-mannose-1-phosphate guanyltransferase activity.
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