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 220.127.116.11.) were examined. Only Na+ increased both phospho-enzyme and [3H] ouabain binding livels 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 effective 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 directly increase the equilibrium level of [3H]-ouabain binding to this enzyme under certain conditions.
|Number of pages||13|
|Journal||BBA - Enzymology|
|State||Published - May 13 1976|
Bibliographical noteFunding Information:
This work was supported by grants from the Michigan Heart Association, Grant H.L. 16055-01 from the National Institutes of Health, grant BMS 74-19512 from the National Science Foundation and General Research Support Grant NIH RR 05623-04 to the College of Veterinary Medicine, Michigan State University, from the National Institutes of Health.
ASJC Scopus subject areas
- Medicine (all)