Photosystem I: towards stable photovoltage generation in a semi-artificial system

The generation of voltage (ΔV) by purified photosynthetic protein-pigment complex of photosystem I (PS I) from the cyanobacterium Synechocystis sp. PCC 6803 immobilized onto a porous Millipore nitrocellulose membrane filter (MF) and contacting with indium tin oxide (ITO) semiconductor glass slides, termed ITO|PS I - MF|ITO have been directly measured. In the presence of the ascorbate/2,6-dichlorophenolindophenol redox couple and disaccharide trehalose, photoinduced generation of ΔV with a maximum amplitude was observed upon light irradiation for more than 1 h. After storing the ITO|PS I - MF|ITO system in a desiccator at 22 ± 1 °C and ~ 65% relative humidity for 7 days in the dark, the photovoltage amplitude decreased by ~ 15%. A significant drop in the ΔV amplitude was observed on the 14th day of storage under these conditions. The amplitude of the stable ΔV signal was fully restored after re-injecting fresh buffer directly into the system, although maximum amplitude was reached more slowly. It is clear that longer preservation of PS I functional activity during storage of the system can be achieved at a higher relative humidity in the desiccator, since the photovoltage was completely suppressed within 24 h when the system was stored in the dark in the laboratory room. The protective role of trehalose is also discussed.