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Electrogenic Binding of Ions at the Cytoplasmic Side of the Na<sup>+</sup>,K<sup>+</sup>-ATPase

Electrogenic Binding of Ions at the Cytoplasmic Side of the Na+,K+-ATPase

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TASHKIN, Vsevolod Yu., A.N. GAVRILCHIK, Alexey I. ILOVAISKY, Hans-Jürgen APELL, Valeriy S. SOKOLOV, 2015. Electrogenic Binding of Ions at the Cytoplasmic Side of the Na+,K+-ATPase. In: Biochemistry (Moscow) Supplement Series A : Membrane and Cell Biology. 9(2), pp. 92-99. ISSN 1990-7478. eISSN 1990-7494

@article{Tashkin2015Elect-31504, title={Electrogenic Binding of Ions at the Cytoplasmic Side of the Na+,K+-ATPase}, year={2015}, doi={10.1134/S1990747815020105}, number={2}, volume={9}, issn={1990-7478}, journal={Biochemistry (Moscow) Supplement Series A : Membrane and Cell Biology}, pages={92--99}, author={Tashkin, Vsevolod Yu. and Gavrilchik, A.N. and Ilovaisky, Alexey I. and Apell, Hans-Jürgen and Sokolov, Valeriy S.} }

Ilovaisky, Alexey I. Electrogenic Binding of Ions at the Cytoplasmic Side of the Na<sup>+</sup>,K<sup>+</sup>-ATPase 2015-07-27T14:58:05Z Tashkin, Vsevolod Yu. Sokolov, Valeriy S. Tashkin, Vsevolod Yu. Apell, Hans-Jürgen Gavrilchik, A.N. Ilovaisky, Alexey I. 2015 2015-07-27T14:58:05Z eng Sokolov, Valeriy S. Gavrilchik, A.N. Electrogenic binding of ions from the cytoplasmic side of the Na<sup>+</sup>,K<sup>+</sup>-ATPase has been studied by measurements of changes of the membrane capacitance and conductance triggered by a jump of pH or of the sodium-ion concentration in the absence of ATP. The pH jumps were performed in experiments with membrane fragments containing purified Na<sup>+</sup>,K<sup>+</sup>-ATPase adsorbed to a bilayer lipid membrane (BLM). Protons were released in a sub-millisecond time range from a photosensitive compound (caged H<sup>+</sup>) triggered by a UV light flash. The sodium concentration jumps were carried out by a fast solution exchange in experiments with membrane fragments attached to a solid-supported membrane deposited on a gold electrode. The change of the membrane capacitance triggered by the pH jump depended on the sodium-ion concentration. Potassium ions had a similar effect on the capacitance change triggered by a pH jump. The effects of these ions are explained by the their competition with protons in the binding sites on cytoplasmic side of the Na<sup>+</sup>,K<sup>+</sup>-ATPase. The approximation of the experimental data by a theoretical model yields the dissociation constants, K, and the cooperativity coefficients, n, of the binding sites for sodium ions (K = 2.7 mM, n = 2) and potassium ions (K = 1.7 mM, n = 2). In the presence of magnesium ions the apparent dissociation constants of sodium increased. A possible reason of the inhibition of sodium-ion binding by magnesium ions can be an electrostatic or conformational effect of magnesium ions bound to a separate site of the Na<sup>+</sup>,K<sup>+</sup>-ATPase close to the entrance to the sodium-ion binding sites. Apell, Hans-Jürgen

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