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Proteoliposomes with right-side-out oriented purple membrane/bacteriorhodopsin require cations inside for proton
1Department of Biology, Faculty of Science, Osaka University, Toyonaka, Japan.
FEBS Letters
|November 21, 1988
Summary
Proteoliposomes with right-side-out bacteriorhodopsin (BR) did not pump protons until cations entered. Proton pumping by BR proteoliposomes depends on cation permeation and bacteriorhodopsin orientation.
Area of Science:
- Biochemistry
- Membrane Biophysics
- Photobiology
Background:
- Purple membranes contain bacteriorhodopsin (BR), a light-driven proton pump.
- Proteoliposomes are vesicles formed from lipids and membrane proteins.
- BR orientation within proteoliposomes affects proton pumping activity.
Purpose of the Study:
- To investigate the factors influencing proton pumping in bacteriorhodopsin proteoliposomes.
- To determine the role of cation concentration and BR orientation in proton translocation.
- To understand the mechanism of light-driven proton pumping in reconstituted systems.
Main Methods:
- Preparation of proteoliposomes by sonication of phospholipids and purple membranes.
- Determination of bacteriorhodopsin orientation using papain digestion.
- Measurement of light-driven proton pumping activity under varying ionic conditions.
Main Results:
- Proteoliposomes predominantly contained right-side-out oriented bacteriorhodopsin.
- Right-side-out BR proteoliposomes showed no proton pumping until cation permeation.
- Inversely oriented BR proteoliposomes exhibited proton pumping activity.
- Proton pumping in right-side-out proteoliposomes initiated upon cation incorporation.
Conclusions:
- Bacteriorhodopsin orientation is critical for light-driven proton pumping in proteoliposomes.
- Cation permeation into the proteoliposome is necessary for proton pumping by right-side-out BR.
- These findings elucidate the mechanism of proton translocation across reconstituted membranes.