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Separation and characterization of Na+,K(+)-ATPase containing vesicles
Ivashchuk-Kienbaum YuA1, H J Apell
1Department of Biology, University of Konstanz, Germany.
Biochimica Et Biophysica Acta
|November 23, 1994
Summary
This study reconstitutes Na+,K(+)-ATPase in vesicles, finding that transport activity ceases at low protein concentrations. This supports the hypothesis that the (alpha beta)2 heterodimer is the active form of this ion pump.
Area of Science:
- Biochemistry
- Membrane Biology
- Enzymology
Background:
- Na+,K(+)-ATPase (sodium-potassium pump) is crucial for cellular ion homeostasis.
- Reconstitution of membrane proteins into vesicles is essential for studying their function.
- Understanding the oligomeric state of Na+,K(+)-ATPase is key to its mechanism.
Purpose of the Study:
- To reconstitute functional Na+,K(+)-ATPase into vesicles.
- To characterize vesicle fractions for enzymatic and transport activity.
- To determine the minimal protein concentration required for transport activity and infer the active oligomeric state.
Main Methods:
- Vesicle reconstitution using a dialysis method.
- Ion-exchange chromatography for vesicle fractionation.
- Optical methods for lipid and protein quantification.
- Fluorescence labeling (5-IAF) to determine protein per vesicle counts.
Main Results:
- Separated vesicle fractions with distinct Na+,K(+)-ATPase enzymatic and transport activities.
- Developed a protocol to quantify 5-IAF labeled pumps per vesicle.
- Observed complete loss of transport activity at low protein concentrations (3.3 µg/mg lipid).
Conclusions:
- The (alpha beta)2 heterodimer is likely the transport-active form of Na+,K(+)-ATPase.
- The developed method is applicable to other reconstituted vesicle systems using fluorescent labeling.