SPECIFIC MODIFICATIONS OF THE Na+, K+‐DEPENDENT ADENOSINE TRIPHOSPHATASE BY DIMETHYL SULFOXIDE*
- 1 January 1975
- journal article
- Published by Wiley in Annals of the New York Academy of Sciences
- Vol. 243 (1), 60-72
- https://doi.org/10.1111/j.1749-6632.1975.tb25344.x
Abstract
DMSO inhibits the Na+, K+-ATPase, but stimulates the associated K+-phosphatase activity. For the ATPase, DMSO acts as an uncompetitive inhibitor toward both ATP and Na+, whereas it increases the K0.5 for K+. From measurements of the dissociation constant (Km) of these ions in the ligand states that correspond to the ATPase reaction, it can be shown that DMSO has little effect on the affinity for Na+, but decreases the affinity for K+ of the enzyme-phosphate intermediate (the form that has the highest affinity for K+). By contrast, DMSO decreases the Km for the phosphatase substrate (nitrophenyl phosphate) without affecting the Vmax. Moreover, DMSO decreases the K0.5 for K+ and also the Kd for K+ in the ligand states that correspond to the phosphatase reaction (which have only a moderate affinity for K+, since the acyl phosphate intermediate is absent in this pathway). These data may be incorporated into a reaction mechanism for the Na+, K+-ATPase. Initially the enzyme is phosphorylated to form an acyl phosphate intermediate, in steps that require Na+ and Mg-2+. At this stage the affinity of K+ is markedly increased (from the moderate affinity seen in the "free" enzyme and the phosphatase reaction). When K+ is bound, the phosphate group is transferred to the hydrolytic site where P-i is ultimately released. DMSO acts at the point at which the acyl phosphate group or the phosphatase substrate enters the hydrolytic site, inhibiting one and facilitating the other. At this stage the affinity for K+ is also changing, and DMSO apparently selects an enyme conformation of intermediate affinity. Ion transport may occur by a gate mechanism in an overall system that operates on a half-of-the-sites active enzyme pattern in which ATP hydrolysis may alternate between the dimeric subunits of the enzyme.Keywords
This publication has 37 references indexed in Scilit:
- Affinity of the (Na+ + K+)‐dependent ATPase for Na+ measured by NA+‐modified enzyme inactivationFEBS Letters, 1974
- Ouabain binding to the sodium pump in plasma membranes isolated from ox brainBiochimica et Biophysica Acta (BBA) - Biomembranes, 1973
- Proposed Reaction Mechanism for the (Na+ + K+)-Dependent Adenosine TriphosphataseNature, 1971
- Active Sodium and Potassium Transport in High Potassium and Low Potassium Sheep Red CellsThe Journal of general physiology, 1971
- Half-of-the-sites reactivity and conformational states of cytidine triphosphate synthetaseBiochemistry, 1971
- K+-stimulated incorporation of 32P from nitrophenyl phosphate into a (Na++K+)-activated ATPase preparationBiochemical and Biophysical Research Communications, 1971
- Potassium-activated phosphatase from human red blood cellsThe Journal of Membrane Biology, 1970
- Effects of ATP and Na+ on a K+-activated phosphatase from red blood cell membranesBiochimica et Biophysica Acta (BBA) - Biomembranes, 1968
- On the interactions of Na+, K+, Mg++, and ATP with the Na+ plus K+ activated ATPase from rat brainBiochemical and Biophysical Research Communications, 1965
- The influence of some cations on an adenosine triphosphatase from peripheral nervesBiochimica et Biophysica Acta, 1957