Electrical Double Layers in Pigment-Containing Biomembranes
Displacement photocurrents are unique to pigment-containing biomembranes. They belong to a special class of bioelectric signals that are generated by rapid charge displacements in the membranes. Interpretation of displacement photocurrents is not straightforward, and direct application of classical electrophysiological methodology is not adequate. However, a more comprehensive understanding of displacement photocurrents can be achieved by applying the Gouy-Chapman diffuse double layer theory to two possible prototype mechanisms of light-induced charge displacements. Macroscopically, a chemical capacitance in addition to the ordinary membrane capacitance must be invoked in the analysis of experimental data. By doing so, some apparent discrepancies of experimental observations can be readily resolved. In this paper, we use the bacteriorhodopsin membrane system to illustrate how the concept of chemical capacitance can assist experimentalists to achieve a meaningful decomposition of a multi-component displacement photocurrent signal. The general applicability of such an approach in other pigment-containing membrane systems of greater complexity is suggested.
KeywordsMembrane Phase Planar Lipid Bilayer Purple Membrane Relaxation Time Constant Interfacial Charge Transfer
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