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. 1999 Feb;76(2):827–836. doi: 10.1016/S0006-3495(99)77246-2

Charge translocation by the Na+/K+-ATPase investigated on solid supported membranes: cytoplasmic cation binding and release.

J Pintschovius 1, K Fendler 1, E Bamberg 1
PMCID: PMC1300084  PMID: 9929484

Abstract

In the preceding publication (. Biophys. J. 76:000-000) a new technique was described that was able to produce concentration jumps of arbitrary ion species at the surface of a solid supported membrane (SSM). This technique can be used to investigate the kinetics of ion translocating proteins adsorbed to the SSM. Charge translocation of the Na+/K+-ATPase in the presence of ATP was investigated. Here we describe experiments carried out with membrane fragments containing Na+/K+-ATPase from pig kidney and in the absence of ATP. Electrical currents are measured after rapid addition of Na+. We demonstrate that these currents can be explained only by a cation binding process on the cytoplasmic side, most probably to the cytoplasmic cation binding site of the Na+/K+-ATPase. An electrogenic reaction of the protein was observed only with Na+, but not with other monovalent cations (K+, Li+, Rb+, Cs+). Using Na+ activation of the enzyme after preincubation with K+ we also investigated the K+-dependent half-cycle of the Na+/K+-ATPase. A rate constant for K+ translocation in the absence of ATP of 0.2-0.3 s-1 was determined. In addition, these experiments show that K+ deocclusion, and cytoplasmic K+ release are electroneutral.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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