title: Interplay of Mg2+, ADP, and ATP in the cytosol and mitochondria: unravelling the role of Mg2+ in cell respiration.
abstract: In animal and plant cells, the ATP/ADP ratio and/or energy charge are generally considered key parameters regulating metabolism and respiration. The major alternative issue of whether the cytosolic and mitochondrial concentrations of ADP and ATP directly mediate cell respiration remains unclear, however. In addition, because only free nucleotides are exchanged by the mitochondrial ADP/ATP carrier, whereas MgADP is the substrate of ATP synthase (EC 3.6.3.14), the cytosolic and mitochondrial Mg(2+) concentrations must be considered as well. Here we developed in vivo/in vitro techniques using (31)P-NMR spectroscopy to simultaneously measure these key components in subcellular compartments. We show that heterotrophic sycamore (Acer pseudoplatanus L.) cells incubated in various nutrient media contain low, stable cytosolic ADP and Mg(2+) concentrations, unlike ATP. ADP is mainly free in the cytosol, but complexed by Mg(2+) in the mitochondrial matrix, where [Mg(2+)] is tenfold higher. In contrast, owing to a much higher affinity for Mg(2+), ATP is mostly complexed by Mg(2+) in both compartments. Mg(2+) starvation used to alter cytosolic and mitochondrial [Mg(2+)] reversibly increases free nucleotide concentration in the cytosol and matrix, enhances ADP at the expense of ATP, decreases coupled respiration, and stops cell growth. We conclude that the cytosolic ADP concentration, and not ATP, ATP/ADP ratio, or energy charge, controls the respiration of plant cells. The Mg(2+) concentration, remarkably constant and low in the cytosol and tenfold higher in the matrix, mediates ADP/ATP exchange between the cytosol and matrix, [MgADP]-dependent mitochondrial ATP synthase activity, and cytosolic free ADP homeostasis.
authors.affiliation: Laboratoire de Physiologie Cellulaire & Végétale, Institut de Recherches en Technologies et Sciences pour le Vivant, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Unité Mixte de Recherche 5168 CNRS, Université Grenoble Alpes (UGA), Institut National de la Recherche Agronomique (INRA), CEA, F-38054 Grenoble, France.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Gout
authors.affiliation: Laboratoire de Physiologie Cellulaire & Végétale, Institut de Recherches en Technologies et Sciences pour le Vivant, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Unité Mixte de Recherche 5168 CNRS, Université Grenoble Alpes (UGA), Institut National de la Recherche Agronomique (INRA), CEA, F-38054 Grenoble, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rébeillé
authors.affiliation: Laboratoire de Physiologie Cellulaire & Végétale, Institut de Recherches en Technologies et Sciences pour le Vivant, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Unité Mixte de Recherche 5168 CNRS, Université Grenoble Alpes (UGA), Institut National de la Recherche Agronomique (INRA), CEA, F-38054 Grenoble, France.
authors.forename: Roland
authors.initials: R
authors.lastname: Douce
authors.affiliation: Laboratoire de Physiologie Cellulaire & Végétale, Institut de Recherches en Technologies et Sciences pour le Vivant, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Unité Mixte de Recherche 5168 CNRS, Université Grenoble Alpes (UGA), Institut National de la Recherche Agronomique (INRA), CEA, F-38054 Grenoble, France rbligny@cea.fr.
authors.forename: Richard
authors.initials: R
authors.lastname: Bligny
mesh_terms: D031002:Acer / Q000166:cytology*; D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D002451:Cell Compartmentation; D002457:Cell Extracts; D019069:Cell Respiration; D003600:Cytosol / Q000378:metabolism*; D006706:Homeostasis; D008274:Magnesium / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D059828:Plant Cells / Q000378:metabolism
chemical_list: D002457:Cell Extracts; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D008274:Magnesium
keywords: 31P-NMR spectroscopy; ADP and Mg2+ homeostasis; cytosolic free ADP; cytosolic free Mg2+; plant cell respiration