Charge Displacements in Interfacial Layers Containing Reaction Centers

Abstract.

Reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides were oriented in phospholipid interfacial layers adsorbed to a Teflon film separating two electrolyte-filled compartments of a Teflon cell. Light-induced voltage changes were measured as a function of time across electrodes immersed in the cell compartments. The experimental system is characterized both experimentally and theoretically to relate the measured signals to the light-induced displacement currents in the reaction centers. Mathematical relations between the measured signals and the distances and geometries of the charge-transfer reactions are derived. At pH 8.0 the reaction centers were found to be oriented with ∼60% of the population oriented with the donor facing the aqueous phase. The density of the reaction centers in the layer was ∼10¹¹ cm⁻², which is close to that found in the native system. Reconstitution of the secondary quinone, Q _B , in 90% of the RCs was achieved with an ∼100-fold excess of ubiquinone in the vesicle preparation.