Article: article from journal or magazin.
Electrogenicity of Na,K- and H,K-ATPase activity and presence of a positively charged amino acid in the fifth transmembrane segment.
Journal of Biological Chemistry
Publication types: Journal Article
The transport activity of the Na,K-ATPase (a 3 Na+ for 2 K+ ion exchange) is electrogenic, whereas the closely related gastric and non-gastric H,K-ATPases perform electroneutral cation exchange. We have studied the role of a highly conserved serine residue in the fifth transmembrane segment of the Na,K-ATPase, which is replaced with a lysine in all known H,K-ATPases. Ouabain-sensitive 86Rb uptake and K+-activated currents were measured in Xenopus oocytes expressing the Bufo bladder H,K-ATPase or the Bufo Na,K-ATPase in which these residues, Lys800 and Ser782, respectively, were mutated. Mutants K800A and K800E of the H,K-ATPase showed K+-stimulated and ouabain-sensitive electrogenic transport. In contrast, when the positive charge was conserved (K800R), no K+-induced outward current could be measured, even though rubidium transport activity was present. Conversely, the S782R mutant of the Na,K-ATPase had non-electrogenic transport activity, whereas the S782A mutant was electrogenic. The K800S mutant of the H,K-ATPase had a more complex behavior, with electrogenic transport only in the absence of extracellular Na+. Thus, a single positively charged residue in the fifth transmembrane segment of the alpha-subunit can determine the electrogenicity and therefore the stoichiometry of cation transport by these ATPases.
Animals, Bufo marinus/genetics, Cell Membrane/enzymology, Electric Conductivity, Electrochemistry, Female, Gene Expression, Lysine, Models, Molecular, Mutagenesis, Site-Directed, Oocytes/enzymology, Ouabain/pharmacology, Potassium/pharmacology, Proton-Translocating ATPases/chemistry, Proton-Translocating ATPases/genetics, Rubidium Radioisotopes/metabolism, Serine/chemistry, Sodium-Potassium-Exchanging ATPase/chemistry, Sodium-Potassium-Exchanging ATPase/genetics, Transfection, Urinary Bladder/enzymology, Xenopus
Web of science
Last modification date