Arabidopsis VTC2 Encodes a GDP-l-Galactose Phosphorylase, the Last Unknown Enzyme in the Smirnoff-Wheeler Pathway to Ascorbic Acid in Plants

The first committed step in the biosynthesis of l-ascorbate from d-glucose in plants requires conversion of GDP-l-galactose to l-galactose 1-phosphate by a previously unidentified enzyme. Here we show that the protein encoded by VTC2, a gene mutated in vitamin C-deficient Arabidopsis thaliana strain...

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Bibliographic Details
Published in:The Journal of biological chemistry 2007-06, Vol.282 (26), p.18879-18885
Main Authors: Linster, Carole L., Gomez, Tara A., Christensen, Kathryn C., Adler, Lital N., Young, Brian D., Brenner, Charles, Clarke, Steven G.
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Arabidopsis - enzymology
Arabidopsis - genetics
Arabidopsis Proteins - genetics
Arabidopsis Proteins - metabolism
Ascorbic Acid - biosynthesis
Ascorbic Acid - metabolism
Galactose - metabolism
Glucose - metabolism
Guanosine Diphosphate - metabolism
Molecular Sequence Data
Phosphoric Monoester Hydrolases - genetics
Phosphoric Monoester Hydrolases - metabolism
Phosphorylases - genetics
Phosphorylases - metabolism
Phosphorylation
Substrate Specificity
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Summary:The first committed step in the biosynthesis of l-ascorbate from d-glucose in plants requires conversion of GDP-l-galactose to l-galactose 1-phosphate by a previously unidentified enzyme. Here we show that the protein encoded by VTC2, a gene mutated in vitamin C-deficient Arabidopsis thaliana strains, is a member of the GalT/Apa1 branch of the histidine triad protein superfamily that catalyzes the conversion of GDP-l-galactose to l-galactose 1-phosphate in a reaction that consumes inorganic phosphate and produces GDP. In characterizing recombinant VTC2 from A. thaliana as a specific GDP-l-galactose/GDP-d-glucose phosphorylase, we conclude that enzymes catalyzing each of the ten steps of the Smirnoff-Wheeler pathway from glucose to ascorbate have been identified. Finally, we identify VTC2 homologs in plants, invertebrates, and vertebrates, suggesting that a similar reaction is used widely in nature.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M702094200