Combined allosteric and competitive interaction between extracellular Na(+) and K(+) during ion transport by the alpha(1), alpha(2), and alpha(3) isoforms of the Na, K-ATPase.
A combined allosteric and competitive model describes the interaction between extracellular Na(+) and Rb(+) during ion transport mediated by the Na, K-ATPase. The model was developed from experiments based on (86)Rb uptake by whole cells transfected with rat isoforms of the enzyme. In the absence of Na(+), only a single transport site for extracellular Rb(+) exists. After the occupation of the Na(+)-specific allosteric site, the Rb(+) transport pocket opens to allow occupation by an additional Rb(+) and the subsequent transport of the two Rb(+) ions into the cells. Na(+) can also directly compete with Rb(+) for binding to at least one of the transport sites. While the model derived here applies to each of the three rat isoforms of the Na, K-ATPase expressed in HeLa cells, subtle differences exist among the isoforms. The alpha(3)* isoform has an increased intrinsic affinity for Rb(+) and a lower affinity for the allosteric Na(+) site than alpha(1) or alpha(2)*. The stimulation of uptake observed according to the best-fit model is due to the displacement by Rb(+) of inhibitory Na(+) bound to the transport site.
Department of Pharmacology and Cell Biophysics, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0575 USA. balshaw@med.unc.edu
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DM
Balshaw
L A
LA
Millette
K
K
Tepperman
E T
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Wallick
D000494:Allosteric Regulation; D000495:Allosteric Site; D000818:Animals; D001667:Binding, Competitive; D006367:HeLa Cells; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism*; D014162:Transfection
D007527:Isoenzymes; D011994:Recombinant Proteins; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium