Reconstructed light-harvesting system for photosynthetic reaction centres

A model of a photosynthetic unit was constructed using purple photosynthetic bacterial reaction centres and either bacteriochlorophyll a or chlorophyll a molecules embedded together in liposome membranes. For such systems, called reconstituted photoreaction units, we measured the fluorescence, fluorescence excitation and absorption spectra. Our results showed that pigments directly incorporated into the lipid bilayer of the liposomes without the support of polypeptides functioned as light-harvesting antennae for the reaction centres. Light energy absorbed by the donors (pigments) was transferred to the accepters (reaction centres). We determined the charge transfer in our system by measuring the light-induced absorbance change and photocurrent response. The system with reconstructed antennae exhibited enhanced efficiency in both the photobleaching of reaction centres at 860 nm and photoelectric conversion. We used the fluorescence-quenching method to investigate the donor-acceptor energy transfer between the membrane-bonded pigments and the reaction centres. From the fluorescence measurements we evaluated a critical donor-acceptor transfer distance of 37-40 Angstrom as sufficient for Forster resonance energy transfer. Our results showed that the constructed model system is promising as a starting point for investigations into the construction of biodevices for conversion of solar energy into electrical energy.