title: Effects of alkali metal cations on phospho-enzyme levels and [3H] ouabain binding to (Na+ + K+)-ATPase.
abstract: The effects of several alkali metal cations on the relationship between steady state phospho-enzyme levels and initial velocity and equilibrium levels of [3H]-ouabain binding to (Na+ + K+)-ATPase (ATP phosphohydrolase EC 3.6.1.3.) were examined. Only Na+ increased both phospho-enzyme and [3H] ouabain binding levels above those observed in the presence of Mg2+ alone. While Na+ stimulated phosphorylation with an apparent Km of about 1 mM, its stimulation of [3H] ouabain binding was biphasic, the lower Km for stimulation corresponding to the Km for formation of phospho-enzyme. Among the other alkali metal cations, potassium, rubidium and lithium were at least eight times more effect in reducing phospho-enzyme levels than in reducing [3H] ouabain binding. This discrepancy is not due to the stability of the enzyme-ouabain complex, nor to any action on the rates of formation or dissociation of the enzyme-ouabain complex. The data thus suggest that [3H] ouabain interacts with the K+, Rb+ or Li+ -enzyme complexes. For Li+, this hypothesis is further supported by the observation that Li+ can cirectly increase the equilibrium level of [3H] ouabain binding to this enzyme under certain conditions.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology; D002414:Cations, Monovalent / Q000494:pharmacology*; D002586:Cesium / Q000494:pharmacology; D006168:Guinea Pigs; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D010042:Ouabain / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D012413:Rubidium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
chemical_list: D002414:Cations, Monovalent; D002586:Cesium; D010042:Ouabain; D008094:Lithium; D012964:Sodium; D000251:Adenosine Triphosphatases; D008274:Magnesium; D012413:Rubidium; D011188:Potassium