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PMID:19339506

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Citation

Torabinejad, J, Donahue, JL, Gunesekera, BN, Allen-Daniels, MJ and Gillaspy, GE (2009) VTC4 is a bifunctional enzyme that affects myoinositol and ascorbate biosynthesis in plants. Plant Physiol. 150:951-61

Abstract

Myoinositol synthesis and catabolism are crucial in many multiceullar eukaryotes for the production of phosphatidylinositol signaling molecules, glycerophosphoinositide membrane anchors, cell wall pectic noncellulosic polysaccharides, and several other molecules including ascorbate. Myoinositol monophosphatase (IMP) is a major enzyme required for the synthesis of myoinositol and the breakdown of myoinositol (1,4,5)trisphosphate, a potent second messenger involved in many biological activities. It has been shown that the VTC4 enzyme from kiwifruit (Actinidia deliciosa) has similarity to IMP and can hydrolyze l-galactose 1-phosphate (l-Gal 1-P), suggesting that this enzyme may be bifunctional and linked with two potential pathways of plant ascorbate synthesis. We describe here the kinetic comparison of the Arabidopsis (Arabidopsis thaliana) recombinant VTC4 with d-myoinositol 3-phosphate (d-Ins 3-P) and l-Gal 1-P. Purified VTC4 has only a small difference in the V(max)/K(m) for l-Gal 1-P as compared with d-Ins 3-P and can utilize other related substrates. Inhibition by either Ca(2+) or Li(+), known to disrupt cell signaling, was the same with both l-Gal 1-P and d-Ins 3-P. To determine whether the VTC4 gene impacts myoinositol synthesis in Arabidopsis, we isolated T-DNA knockout lines of VTC4 that exhibit small perturbations in abscisic acid, salt, and cold responses. Analysis of metabolite levels in vtc4 mutants showed that less myoinositol and ascorbate accumulate in these mutants. Therefore, VTC4 is a bifunctional enzyme that impacts both myoinositol and ascorbate synthesis pathways.

Links

PubMed PMC2689953 Online version:10.1104/pp.108.135129

Keywords

Arabidopsis/drug effects; Arabidopsis/enzymology; Arabidopsis/growth & development; Ascorbic Acid/biosynthesis; Biocatalysis/drug effects; Cold Temperature; DNA, Bacterial/genetics; Germination/drug effects; Hydrogen-Ion Concentration/drug effects; Inositol/biosynthesis; Kinetics; Magnesium/pharmacology; Metabolic Networks and Pathways/drug effects; Metabolome/drug effects; Mutagenesis, Insertional/drug effects; Mutation/genetics; Phosphoric Monoester Hydrolases/isolation & purification; Phosphoric Monoester Hydrolases/metabolism; Recombinant Proteins/metabolism; Substrate Specificity/drug effects

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

ARATH:HIS7

involved_in

GO:0000105: histidine biosynthetic process

ECO:0000316: genetic interaction evidence used in manual assertion

P

Seeded From UniProt

complete

ARATH:HIS7

enables

GO:0004401: histidinol-phosphatase activity

ECO:0000316: genetic interaction evidence used in manual assertion

F

Seeded From UniProt

complete

ARATH:HIS7

enables

GO:0052834: inositol monophosphate phosphatase activity

ECO:0000316: genetic interaction evidence used in manual assertion

F

Seeded From UniProt

complete

ARATH:IMPL1

enables

GO:0008934: inositol monophosphate 1-phosphatase activity

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete

ARATH:VTC4

acts_upstream_of_or_within

GO:0006021: inositol biosynthetic process

ECO:0000315: mutant phenotype evidence used in manual assertion

P

Seeded From UniProt

complete

ARATH:VTC4

acts_upstream_of_or_within

GO:0009409: response to cold

ECO:0000315: mutant phenotype evidence used in manual assertion

P

Seeded From UniProt

complete

ARATH:VTC4

enables

GO:0008934: inositol monophosphate 1-phosphatase activity

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete

ARATH:VTC4

enables

GO:0010347: L-galactose-1-phosphate phosphatase activity

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete


See also

References

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