Photovoltaic Properties of Spinach Photosystem I Reaction Centers in Solution

Photosystem I (PSI) is one of the photosynthetic reaction centers that converts light energy into electrical and chemical energy. We report on two different experimental techniques to measure the open and closed circuit photovoltaic properties of PSI reaction centers in an aqueous environment. The combined techniques of atomic force microscopy and scanning surface probe microscopy were used to measure the light induced electrostatic surface potentials at the gas-liquid interface. The orientation and magnitude of the light-induced photovoltages of PSI entrained in the pores of microchannel glass plates were recorded. A simple photocatalytic hydrogen-evolving system based on intermolecular electron transfer using isolated PSI reaction centers as the photoactive element is also reported. The experimental system comprised of sodium ascorbate as a sacrificial electron donor, plastocyanin (PC), PSI and sodium hexachloroplatinate. Photodependent platinization of PSI resulted in the formation of an efficient hydrogen evolving