title: Regulation by magnesium of potato tuber mitochondrial respiratory activities.
abstract: Dehydrogenase activities of potato tuber mitochondria and corresponding phosphorylation rates were measured for the dependence on external and mitochondrial matrix Mg2+. Magnesium stimulated state 3 and state 4 respiration, with significantly different concentrations of matrix Mg2+ required for optimal activities of the several substrates. Maximal stimulation of respiration with all substrates was obtained at 2-mM external Mg2+. However, respiration of malate, citrate, and alpha-ketoglutarate requires at least 4-mM Mg2+ inside mitochondria for maximization of dehydrogenase activities. The phosphorylation system, requires a low level of internal Mg2+ (0.25 mM) to reach high activity, as judged by succinate-dependent respiration. However, mitochondria respiring on citrate or alpha-ketoglutarate only sustain high levels of phosphorylation with at least 4-mM matrix Mg2+. Respiration of succinate is active without external and matrix Mg2+, although stimulated by the cation. Respiration of alpha-ketoglutarate was strictly dependent on external Mg2+ required for substrate transport into mitochondria, and internal Mg2+ is required for dehydrogenase activity. Respiration of citrate and malate also depend on internal Mg2+ but, unlike alpha-ketoglutarate, some activity still remains without external Mg2+. All the substrates revealed insensitive to external and internal mitochondrial Ca2+, except the exogenous NADH dehydrogenase, which requires either external Ca2+ or Mg2+ for detectable activity. Calcium is more efficient than Mg2+, both having cumulative stimulation. Unlike Ca2+, Mn2+ could substitute for Mg2+, before and after addition of A23, showing its ability to regulate phosphorylation and succinate dehydrogenase activities, with almost the same efficiency as Mg2+.
authors.affiliation: Departamento de Botânica, Universidade de Coimbra, Coimbra, Portugal. jvicente@ci.uc.pt
authors.forename: Joaquim A F
authors.initials: JA
authors.lastname: Vicente
authors.forename: Vítor M C
authors.initials: VM
authors.lastname: Madeira
authors.forename: Anibal E
authors.initials: AE
authors.lastname: Vercesi
mesh_terms: D002118:Calcium / Q000378:metabolism; D019069:Cell Respiration / Q000187:drug effects / Q000502:physiology; D019343:Citric Acid / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007656:Ketoglutaric Acids / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D008293:Malates / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D008933:Mitochondrial Swelling / Q000502:physiology; D010088:Oxidoreductases / Q000378:metabolism; D010766:Phosphorylation; D035281:Plant Tubers / Q000378:metabolism* / Q000502:physiology; D011198:Solanum tuberosum / Q000378:metabolism* / Q000502:physiology; D019802:Succinic Acid / Q000378:metabolism
chemical_list: D007656:Ketoglutaric Acids; D008293:Malates; D019343:Citric Acid; C030298:malic acid; D019802:Succinic Acid; D010088:Oxidoreductases; D008274:Magnesium; D002118:Calcium