Three distinct and sequential steps in the release of sodium ions by the Na+/K+-ATPase

Miguel Holmgren (), Jonathan Wagg, Francisco Bezanilla, Robert F. Rakowski, Paul De Weer and David C. Gadsby ()
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Miguel Holmgren: The Marine Biological Laboratory
Jonathan Wagg: The Marine Biological Laboratory
Francisco Bezanilla: The Marine Biological Laboratory
Robert F. Rakowski: The Marine Biological Laboratory
Paul De Weer: The Marine Biological Laboratory
David C. Gadsby: The Marine Biological Laboratory

Nature, 2000, vol. 403, issue 6772, 898-901

Abstract: Abstract The Na+/K+ pump, a P-type ion-motive ATPase, exports three sodium ions and then imports two potassium ions in each transport cycle. Ions on one side of the membrane bind to sites within the protein and become temporarily occluded (trapped within the protein) before being released to the other side1,2, but details of these occlusion and de-occlusion transitions remain obscure for all P-type ATPases. If it is deprived of potassium ions, the Na+/K+ pump is restricted to sodium translocation steps3, at least one involving charge movement through the membrane's electric field4,5. Changes in membrane potential alter the rate of such electrogenic reactions and so shift the distribution of enzyme conformations. Here we use high-speed voltage jumps to initiate this redistribution and show that the resulting pre-steady-state charge movements relax in three identifiable phases, apparently reflecting de-occlusion and release of the three sodium ions. Reciprocal relationships among the sizes of these three charge components show that the three sodium ions are de-occluded and released to the extracellular solution one at a time, in a strict order.

Date: 2000
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DOI: 10.1038/35002599

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