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pH-induced proton permeability changes of plasma membrane vesicles
H Miedema1, M Staal, H B Prins
1Department of Plant Biology, Laboratory of Plant Physiology, Biological Centre, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands.
The Journal of Membrane Biology
|July 1, 1996
Summary
Isolated plant plasma membrane vesicles show pH-dependent proton permeability, similar to intact Elodea leaves. However, vesicle proton permeability is significantly lower, suggesting loss of transport systems during preparation.
Area of Science:
- Plant Physiology
- Membrane Biophysics
- Biochemistry
Background:
- In vivo studies indicate Elodea nuttallii plasma membrane proton permeability is highly pH-dependent.
- The behavior of isolated plasma membrane vesicles regarding proton permeability remains less understood.
Purpose of the Study:
- To investigate if isolated plasma membrane vesicles exhibit pH-dependent proton permeability.
- To quantify proton fluxes and permeability coefficients in response to pH changes.
Main Methods:
- Utilized acridine orange to measure passive proton fluxes across right-side out vesicles.
- Applied pH jumps to vesicles and calculated proton permeability coefficients (PH+) from the decay of the applied DeltapH.
Main Results:
- Proton permeability of vesicle membranes was found to be pH-sensitive, influenced by both internal and external pH.
- Under symmetric conditions, proton permeability increased significantly with external pH.
- Calculated proton permeability values in vesicles were orders of magnitude lower than in intact leaves.
Conclusions:
- Isolated plasma membrane vesicles retain pH-dependent proton permeability, but at reduced levels compared to intact tissues.
- The diminished permeability suggests the loss or inactivation of key transport systems during vesicle isolation.
- The residual permeability likely reflects the intrinsic proton permeability of the phospholipid bilayer.