Enzymes
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- Name help_outline α-D-mannose 1-phosphate Identifier CHEBI:58409 (Beilstein: 3911528) help_outline Charge -2 Formula C6H11O9P InChIKeyhelp_outline HXXFSFRBOHSIMQ-RWOPYEJCSA-L SMILEShelp_outline OC[C@H]1O[C@H](OP([O-])([O-])=O)[C@@H](O)[C@@H](O)[C@@H]1O 2D coordinates Mol file for the small molecule Search links Involved in 12 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline GDP-α-D-glucose Identifier CHEBI:62230 Charge -2 Formula C16H23N5O16P2 InChIKeyhelp_outline MVMSCBBUIHUTGJ-LRJDVEEWSA-L SMILEShelp_outline Nc1nc2n(cnc2c(=O)[nH]1)[C@@H]1O[C@H](COP([O-])(=O)OP([O-])(=O)O[C@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@H]2O)[C@@H](O)[C@H]1O 2D coordinates Mol file for the small molecule Search links Involved in 8 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline α-D-glucose 1-phosphate Identifier CHEBI:58601 (Beilstein: 3560164) help_outline Charge -2 Formula C6H11O9P InChIKeyhelp_outline HXXFSFRBOHSIMQ-VFUOTHLCSA-L SMILEShelp_outline OC[C@H]1O[C@H](OP([O-])([O-])=O)[C@H](O)[C@@H](O)[C@@H]1O 2D coordinates Mol file for the small molecule Search links Involved in 41 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline GDP-α-D-mannose Identifier CHEBI:57527 (Beilstein: 6630718) help_outline Charge -2 Formula C16H23N5O16P2 InChIKeyhelp_outline MVMSCBBUIHUTGJ-GDJBGNAASA-L SMILEShelp_outline Nc1nc2n(cnc2c(=O)[nH]1)[C@@H]1O[C@H](COP([O-])(=O)OP([O-])(=O)O[C@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@@H]2O)[C@@H](O)[C@H]1O 2D coordinates Mol file for the small molecule Search links Involved in 54 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
Cross-references
| RHEA:66032 | RHEA:66033 | RHEA:66034 | RHEA:66035 | |
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| Reaction direction help_outline | undefined | left-to-right | right-to-left | bidirectional |
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Publications
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The VTC2 cycle and the de novo biosynthesis pathways for vitamin C in plants: an opinion.
Wolucka B.A., Van Montagu M.
The recent identification of the VTC2 enzyme (GDP-l-galactose: hexose 1-phosphate guanylyltransferase) that forms with the GDP-mannose 3'',5'' epimerase an energy-conserving hub for the production of GDP-hexoses and l-galactose 1-phosphate [Laing et al., Proc. Natl. Acad. Sci. USA 104, 2007, 9534- ... >> More
The recent identification of the VTC2 enzyme (GDP-l-galactose: hexose 1-phosphate guanylyltransferase) that forms with the GDP-mannose 3'',5'' epimerase an energy-conserving hub for the production of GDP-hexoses and l-galactose 1-phosphate [Laing et al., Proc. Natl. Acad. Sci. USA 104, 2007, 9534-9539], is a major breakthrough in our understanding of the biosynthesis of l-ascorbic acid (vitamin C) in plants. The observation that the VTC2 enzyme can use glucose 1-phosphate and GDP-d-glucose as substrates, and the long-known existence of an enigmatic GDP-d-mannose 2''-epimerase activity, have led us to the proposal of an extended VTC2 cycle that links photosynthesis with the biosynthesis of vitamin C and the cell-wall metabolism in plants. An evolutionary scenario is discussed for the acquisition of genes of eubacterial origin for the de novo synthesis of l-ascorbic acid in green algae and plants. << Less
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A second GDP-L-galactose phosphorylase in arabidopsis en route to vitamin C. Covalent intermediate and substrate requirements for the conserved reaction.
Linster C.L., Adler L.N., Webb K., Christensen K.C., Brenner C., Clarke S.G.
The Arabidopsis thaliana VTC2 gene encodes an enzyme that catalyzes the conversion of GDP-L-galactose to L-galactose 1-phosphate in the first committed step of the Smirnoff-Wheeler pathway to plant vitamin C synthesis. Mutations in VTC2 had previously been found to lead to only partial vitamin C d ... >> More
The Arabidopsis thaliana VTC2 gene encodes an enzyme that catalyzes the conversion of GDP-L-galactose to L-galactose 1-phosphate in the first committed step of the Smirnoff-Wheeler pathway to plant vitamin C synthesis. Mutations in VTC2 had previously been found to lead to only partial vitamin C deficiency. Here we show that the Arabidopsis gene At5g55120 encodes an enzyme with high sequence identity to VTC2. Designated VTC5, this enzyme displays substrate specificity and enzymatic properties that are remarkably similar to those of VTC2, suggesting that it may be responsible for residual vitamin C synthesis in vtc2 mutants. The exact nature of the reaction catalyzed by VTC2/VTC5 is controversial because of reports that kiwifruit and Arabidopsis VTC2 utilize hexose 1-phosphates as phosphorolytic acceptor substrates. Using liquid chromatography-mass spectroscopy and a VTC2-H238N mutant, we provide evidence that the reaction proceeds through a covalent guanylylated histidine residue within the histidine triad motif. Moreover, we show that both the Arabidopsis VTC2 and VTC5 enzymes catalyze simple phosphorolysis of the guanylylated enzyme, forming GDP and L-galactose 1-phosphate from GDP-L-galactose and phosphate, with poor reactivity of hexose 1-phosphates as phosphorolytic acceptors. Indeed, the endogenous activities from Japanese mustard spinach, lemon, and spinach have the same substrate requirements. These results show that Arabidopsis VTC2 and VTC5 proteins and their homologs in other plants are enzymes that guanylylate a conserved active site His residue with GDP-L-galactose, forming L-galactose 1-phosphate for vitamin C synthesis, and regenerate the enzyme with phosphate to form GDP. << Less
J. Biol. Chem. 283:18483-18492(2008) [PubMed] [EuropePMC]
This publication is cited by 2 other entries.
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Arabidopsis VTC2 encodes a GDP-L-galactose phosphorylase, the last unknown enzyme in the Smirnoff-Wheeler pathway to ascorbic acid in plants.
Linster C.L., Gomez T.A., Christensen K.C., Adler L.N., Young B.D., Brenner C., Clarke S.G.
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 stra ... >> More
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. << Less
J. Biol. Chem. 282:18879-18885(2007) [PubMed] [EuropePMC]
This publication is cited by 2 other entries.