Light induced dipole layers in the thylakoid membrane

Abstract

From the characteristics of the light induced spectral changes of the bulk dyes in the thylakoid membrane, it is shown that the rate limiting step of valinomycin facilitated potassium transport across the thylakoid membrane is the dissociation of the ion carrier complex at the surface of the membrane. Junge & Schmid (1971) reported a hyperbolic sine relation between the magnitude of the light induced spectral changes and their initial decay rate after short flashes of light of varying intensity. A simple theoretical model is derived based on the generation of two dipole layers at the surfaces of the membrane that exhibits the hyperbolic sine behavior. This model allows one to calculate a light induced surface potential change of 80 mV at each surface of the membrane and to estimate an effective surface capacitance on the order of 140 μF/cm−2. A simple equivalent circuit is proposed that relates the surface charge displacements to the apparent transmembrane transport of protonic and other ionic charge carriers and relates the decay rate of the light induced absorbance change to the appropriate membrane parameters.