The Isoenzyme 7 of Tobacco NAD(H)-Dependent Glutamate Dehydrogenase Exhibits High Deaminating and Low Aminating Activities in Vivo
- 11 October 2007
- journal article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 145 (4), 1726-1734
- https://doi.org/10.1104/pp.107.107813
Abstract
Following the discovery of glutamine synthetase/glutamate (Glu) synthase, the physiological roles of Glu dehydrogenase (GDH) in nitrogen metabolism in plants remain obscure and is the subject of considerable controversy. Recently, transgenics were used to overexpress the gene encoding for the beta-subunit polypeptide of GDH, resulting in the GDH-isoenzyme 1 deaminating in vivo Glu. In this work, we present transgenic tobacco (Nicotiana tabacum) plants overexpressing the plant gdh gene encoding for the alpha-subunit polypeptide of GDH. The levels of transcript correlated well with the levels of total GDH protein, the alpha-subunit polypeptide, and the abundance of GDH-anionic isoenzymes. Assays of transgenic plant extracts revealed high in vitro aminating and low deaminating activities. However, gas chromatography/mass spectrometry analysis of the metabolic fate of (15)NH(4) or [(15)N]Glu revealed that GDH-isoenzyme 7 mostly deaminates Glu and also exhibits low ammonium assimilating activity. These and previous results firmly establish the direction of the reactions catalyzed by the anionic and cationic isoenzymes of GDH in vivo under normal growth conditions and reveal a paradox between the in vitro and in vivo enzyme activities.Keywords
This publication has 29 references indexed in Scilit:
- Tobacco Isoenzyme 1 of NAD(H)-Dependent Glutamate Dehydrogenase Catabolizes Glutamate in VivoPlant Physiology, 2006
- Abiotic Stress Generates ROS That Signal Expression of Anionic Glutamate Dehydrogenases to Form Glutamate for Proline Synthesis in Tobacco and GrapevinePlant Cell, 2006
- NADP‐dependent glutamate dehydrogenase: a dispensable function in ectomycorrhizal fungiNew Phytologist, 2005
- Genetic and Physiological Analysis of Germination Efficiency in Maize in Relation to Nitrogen Metabolism Reveals the Importance of Cytosolic Glutamine SynthetasePlant Physiology, 2002
- Cloning and characterisation of a glutamate dehydrogenase cDNA from tomato (Lycopersicon esculentum L.)Gene, 1997
- Plant NAD(H)-Glutamate Dehydrogenase Consists of Two Subunit Polypeptides and Their Participation in the Seven Isoenzymes Occurs in an Ordered RatioPlant Physiology, 1991
- Kinetics of 15NH4+ Assimilation in Zea maysPlant Physiology, 1990
- Immunocharacterization of NADH-Glutamate Dehydrogenase from Vitis vinifera LPlant Physiology, 1990
- Synthesis of [15N]Glutamate from [15N]H4+ and [15N]Glycine by Mitochondria Isolated from Pea and Corn ShootsPlant Physiology, 1986
- Alternative route for nitrogen assimilation in higher plantsNature, 1974