title: A 31P-NMR study of the mechanism of and salt effect on Mg2(+)-ATP exchange.
abstract: The study of exchange between free and metal-bound ligands by NMR methods is discussed with reference to differentiation between unimolecular dissociation of the metal-bound complex and biomolecular exchange of metal ion between two ligands. This is applied to exchange of ATP4- between the free and Mg2(+)-bound states and problems of interpretation in the presence of a strong kinetic salt effect are discussed. Contrary to a previous report, exchange is inferred to occur mainly via unimolecular dissociation of MgATP2- over a range of temperatures, concentrations, and pH values, which include those expected in vivo. For the model system Mg2(+)-tripolyphosphate, an activation energy of 52 +/- 5 kJ.mol-1, inferred to be that for dissociation of MgTPPH2-, is found for the exchange process.
authors: School of Chemistry and Molecular Sciences, University of Sussex, Brighton, U.K.
authors: E O
authors: EO
authors: Bishop
authors: R
authors: R
authors: Miles
authors: B E
authors: BE
authors: Smith
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D010759:Phosphorus Isotopes; D013816:Thermodynamics
chemical_list: D010759:Phosphorus Isotopes; D015636:Magnesium Chloride; D017301:Ca(2+) Mg(2+)-ATPase