Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/6/1997
Publication Date: N/A
Technical Abstract: The problem of predicting the kinetics of the decay of the internal proton concentration for vesicles containing one or more buffers and for which a pH gradient exists across the membrane is examined. The solution builds on earlier work describing proton efflux (J. Whitmarsh (1987) Photosynth. Res. 12:43-62) that was successfully applied to chromatophores from Rhodobacter capsulatus (M.P. Turina, G. Venturoli & B. Melandri (1990) Eur. J. Biochem 192:39-47). An analytical solution is derived that describes the time course of the proton efflux and hydroxyl influx and the internal proton concentration under conditions of zero transmembrane electric potential. The effect of the internal buffers is to increase the time required for the proton/hydroxyl gradient to equilibrate across the membrane. For a vesicle containing a single buffer the solution requires seven independent physical parameters: the initial internal proton concentration, the external proton concentration, the ratio of the vesicle surface area to the internal volume, the permeability coefficients of the membrane for protons and for hydroxyl ions, the total concentration of the internal buffer, and the equilibrium constant for the dissociation of the internal buffer. Determination of these physical values is sufficient to predict the time dependence of the internal proton concentration and of the proton/hydroxyl ion efflux and influx. The theory is applied to plant vacuoles and accounts for the long life (many hours) of pH gradients observed across the tonoplast membrane in the apparent absence of active transport.