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The search for the endogenous digitalis: an alternative hypothesis
The American Journal of Physiology
|May 1, 1989
Summary
A potential endogenous hormone binding to Na+-K+-ATPase may exist within cells, not on the cell membrane. This intracellular ligand could regulate protein function and assembly before membrane insertion.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- The Na+-K+-ATPase enzyme has a binding site for cardiac glycosides, suggesting a potential role for endogenous ligands.
- Speculation exists that this site may bind an endogenous digitalis-like hormone involved in sodium homeostasis and diseases like hypertension.
Purpose of the Study:
- To challenge the hypothesis of an extracellular endogenous ligand for the cardiac glycoside binding site on Na+-K+-ATPase.
- To propose an alternative hypothesis for the evolutionary conservation of this binding site.
Main Methods:
- The study is primarily theoretical, analyzing the known functions and cellular localization of Na+-K+-ATPase.
- It considers the topological equivalence of intracellular organelle lumens to the extracellular space.
Main Results:
- The hypothesis of an extracellular hormone binding to Na+-K+-ATPase is questioned due to its unusual mechanism for a hormone.
- An alternative hypothesis suggests the endogenous ligand is intracellular, potentially regulating Na+-K+-ATPase before cell membrane insertion.
Conclusions:
- The cardiac glycoside binding site on Na+-K+-ATPase may bind an intracellular ligand.
- This intraorganellar ligand could play roles in protein targeting, conformation monitoring, and catalytic regulation during Na+-K+-ATPase biogenesis.