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A slow interconversion between active and inactive states of the (Na-K)ATPase
Biochemistry
|November 30, 1976
Summary
This study reveals that slow conformational changes affect the activity of dog kidney sodium-potassium adenosine triphosphatase (Na-K)ATPase. Ligand concentrations influence enzyme inactivation and reactivation rates due to these slow binding steps.
Area of Science:
- Biochemistry
- Enzymology
- Membrane Transport
Background:
- The sodium-potassium adenosine triphosphatase (Na-K)ATPase is a crucial ion pump in cell membranes.
- Understanding its kinetic properties is vital for comprehending cellular energy metabolism and ion homeostasis.
Purpose of the Study:
- To investigate the slow kinetic changes in Na-K)ATPase activity.
- To elucidate the role of specific ligands (Mg2+, Mg-ATP, K+, Na+) in enzyme function and regulation.
Main Methods:
- Purification of dog kidney Na-K)ATPase.
- Enzymatic assays measuring ATP hydrolysis rates under varying ligand concentrations.
- Kinetic analysis to model enzyme behavior.
Main Results:
- ATP hydrolysis rate is influenced by a rapid ligand binding followed by a slow conformational change.
- Enzyme inactivation occurs with specific ligand concentrations (free Mg2+, Mg-ATP, K+).
- Reactivation is possible by reducing these ligand concentrations, indicating time-dependent affinities.
Conclusions:
- A kinetic model explains the impact of free Mg2+ and Mg-ATP on (Na-K)ATPase activity.
- Slow conformational changes are key determinants of enzyme turnover and regulation.
- Ligand-induced inactivation and reactivation are linked to the enzyme's conformational dynamics.