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Variable stoichiometry in reconstituted shark Na,K-ATPase engaged in uncoupled efflux
1Institute of Biophysics, University of Aarhus, Denmark.
Biochimica Et Biophysica Acta
|July 24, 1990
Summary
Shark Na,K-ATPase pumps exhibit an uncoupled sodium efflux when external sodium and ATP are added. The ratio of sodium transported per ATP split varies with pH and sodium concentration.
Area of Science:
- Biochemistry
- Membrane Transport
- Enzymology
Background:
- The Na,K-adenosine triphosphatase (Na,K-ATPase) is a crucial ion pump in cell membranes.
- Understanding its transport stoichiometry is vital for comprehending cellular ion homeostasis.
Purpose of the Study:
- To investigate the transport stoichiometry of shark Na,K-ATPase under varying conditions.
- To determine the coupling ratio of sodium transport to ATP hydrolysis.
Main Methods:
- Reconstitution of shark Na,K-ATPase into liposomes.
- Measurement of electrogenic sodium efflux coupled to ATP hydrolysis.
- Varying external sodium concentrations and pH levels.
Main Results:
- Addition of external Na+ and ATP induced an uncoupled Na+ efflux in inside-out oriented pumps.
- At saturating cytoplasmic Na+, the Na+/ATP ratio was 3:1 at pH ≥ 7.0, decreasing to 1.5:1 below pH 7.0.
- At non-saturating cytoplasmic Na+, the 3:1 stoichiometry was observed between pH 7.0-7.5, decreasing outside this range.
Conclusions:
- The stoichiometry of shark Na,K-ATPase is sensitive to both pH and cytoplasmic sodium concentration.
- These findings provide insights into the dynamic nature of ion transport mechanisms.