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Biochemical and biological characterization of myo‐inositol monophosphatase in Arabidopsis
Author(s) -
Donahue Janet L,
Torabinejad Javad,
Gunesekera Bhadra,
Gillaspy Glenda
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a256-d
Subject(s) - arabidopsis , inositol , phosphofructokinase 2 , biochemistry , mutant , second messenger system , arabidopsis thaliana , enzyme , biology , gene , biological pathway , chemistry , gene expression , receptor
Myo ‐inositol monophosphatase (IMP) is a major enzyme required for the synthesis of myo ‐inositol and breakdown of inositol (1,4,5)‐trisphosphate, a potent second messenger involved in many biological activities. It has been shown that kiwifruit IMP can also hydrolyze L‐galactose 1‐phosphate (L‐gal 1‐P), linking IMP with two pathways of plant ascorbate synthesis. Our work addresses similar genes in Arabidopsis and their biological functions. We overexpressed the Arabidopsis IMP and the two IMP‐like genes in E. coli and demonstrated that all three genes encode active IMP enzymes. The purified IMP had twice the V max /K m with L‐gal 1‐P compared to myo ‐inositol 1‐P (Inos 1‐P), and can utilize other related substrates. IMP inhibition by either Ca 2+ or Li 2+ , ions known to disrupt cell signaling, was the same with both L‐gal 1‐P and Inos 1‐P substrates. To identify the biological functions of the IMP genes in Arabidopsis, we isolated three knockout lines of IMP exhibiting no obvious phenotype. However, analysis of metabolite levels in imp mutants showed less myo ‐inositol and ascorbate, but more L‐gal than in wildtype plants. Therefore, IMP is a bifunctional enzyme that impacts both ascorbate synthesis pathways. NSF award to G.G. (MCB#0316705).