title: Modulation of the Na,K-ATPase by Magnesium Ions.
abstract: Since the beginning of investigations of the Na,K-ATPase, it has been well-known that Mg2+is an essential cofactor for activation of enzymatic ATP hydrolysis without being transported through the cell membrane. Moreover, experimental evidence has been collected through the years that shows that Mg2+ions have a regulatory effect on ion transport by interacting with the cytoplasmic side of the ion pump. Our experiments allowed us to reveal the underlying mechanism. Mg2+is able to bind to a site outside the membrane domain of the protein's α subunit, close to the entrance of the access channel to the ion-binding sites, thus modifying the local concentration of the ions in the electrolyte, of which Na+, K+, and H+are of physiological interest. The decrease in the concentration of these cations can be explained by electrostatic interaction and estimated by the Debye-Hückel theory. This effect provokes the observed apparent reduction of the binding affinity of the binding sites of the Na,K-ATPase in the presence of various Mg2+concentrations. The presence of the bound Mg2+, however, does not affect the reaction kinetics of the transport function of the ion pump. Therefore, stopped-flow experiments could be performed to gain the first insight into the Na+binding kinetics on the cytoplasmic side by Mg2+concentration jump experiments.
authors.affiliation: Department of Biology, University of Konstanz , 78464 Konstanz, Germany.
authors.forename: Hans-Jürgen
authors.identifier: 0000-0001-8489-0706
authors.initials: HJ
authors.lastname: Apell
authors.affiliation: Department of Biology, University of Konstanz , 78464 Konstanz, Germany.
authors.forename: Tanja
authors.initials: T
authors.lastname: Hitzler
authors.affiliation: Department of Biology, University of Konstanz , 78464 Konstanz, Germany.
authors.forename: Grischa
authors.initials: G
authors.lastname: Schreiber
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002412:Cations / Q000378:metabolism; D003593:Cytoplasm; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D002412:Cations; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium