IAL   21557
INSTITUTO DE AGROBIOTECNOLOGIA DEL LITORAL
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Understanding the Fate of Trioses-phosphate in Plant Cells. A study on the regulation of glyceraldehydes-3-phosphate dehydrogenases
Autor/es:
A.A. IGLESIAS, C.V. PIATTONI, S.A. GUERRERO
Lugar:
Mérida, Yucatán, México
Reunión:
Simposio; Joint Meeting of the American Society of Plant Biologists and the Sociedad Mexicana de Bioquímica; 2008
Institución organizadora:
Aerican Society of Plant Biologists
Resumen:
Minisymposium 3: Metabolism Abs # M0302: Understanding the fate of trioses-phosphate in plant cells. A study on the regulation of cytosolic glyceraldehyde-3-phosphate dehydrogenases Presenter: Iglesias, Alberto A       Contact Presenter Authors Iglesias, Alberto A (A)   Piattoni, Claudia V (A)   Guerrero, Sergio A (A)   Affiliations: (A): Lab. Enzimologia Molecular. Fac. Bioquimica Cs. Biologicas. Universidad Nacional del Litoral Oxidation of glyceraldehyde-3P to 3P-glycerate in the cytosol of plant cells can follow two different pathways. One, involves phosphorylating glyceraldehyde-3P dehydrogenase (Ga3PDHase, EC 1.2.1.12) and 3P-glycerate kinase. The other pathway occurs via non-phosphorylating glyceraldehyde-3P dehydrogenase (npGa3PDHase; EC 1.2.1.9), an enzyme found in photosynthetic eukaryotes. In green cells, npGa3PDHase is involved in a shuttle system to export chloroplastic NADPH. In non-green tissues, the role of the enzyme is less clear; although it catalyzes a critical metabolic branch point in glycolysis, where trioses-P are derived to produce NADPH as an alternative to the synthesis of ATP and NADH. We characterized the post-translational regulation of wheat npGa3PDHase by two mechanisms: phosphorylation of serine residues and redox modification of cysteines. The recombinant enzyme was phosphorylated after incubation with wheat endosperm extracts, under reaction conditions specific for SNF1-related protein kinases. The modification was inhibited by glucose-6P, as was previously reported for protein kinases involved in regulation of carbon metabolism in plants. Phosphorylation was neither observed by other plant protein kinases, nor by incubation with leaf extracts. Site directed mutagenesis studies showed that Ser-404 is the amino acid residue phosphorylated in npGa3PDHase. These results agree with previous data showing that in heterotrophic plant cells the enzyme exhibits distinctive regulatory properties associated with phosphorylation and interaction with 14-3-3 proteins. On the other hand, npGa3PDHase from wheat was inactivated by thiol oxidants as diamide, hydrogen peroxide, sodium nitroprusiate, and oxidized gluthation. The loss of activity was effectively reversed after incubation with dithiothreitol and reduced thioredoxin, thus suggesting that the process could function physiologically. Ga3PDHase was markedly more sensitive to thiol oxidants (and also more resistant to reactivation by reductants) than npGa3PDHase. It is tempting to speculate that under oxidative conditions in the cytosol of plant cells, the fate of trioses-P is preferably derived to NADPH generation rather than to ATP. Results support a scenario where the oxidation of trioses-P is a key metabolic point to regulate the carbon partitioning to produce redox or energy equivalents in the cytosol of plant cells. Work granted by CONICET, ANPCyT and UNL (Argentina).