RECONSTRUCTED LIGHT-HARVESTING SYSTEM FOR PHOTOSYNTHETIC REACTION CENTERS

A model of a photosynthetic unit was constructed using purple photosyn thetic bacterial reaction centres and either bacteriochlorophyll a or chlorophyll a molecules embedded together in liposome membranes. For s uch systems, called reconstituted photoreaction units, we measured the fluorescence, fluorescence excitation and absorption spectra. Our res ults showed that pigments directly incorporated into the lipid bilayer of the liposomes without the support of polypeptides functioned as li ght-harvesting antennae for the reaction centres. Light energy absorbe d 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 sy stem with reconstructed antennae exhibited enhanced efficiency in both the photobleaching of reaction centres at 860 nm and photoelectric co nversion. We used the fluorescence-quenching method to investigate the donor-acceptor energy transfer between the membrane-bonded pigments a nd the reaction centres. From the fluorescence measurements we evaluat ed a critical donor-acceptor transfer distance of 37-40 Angstrom as su fficient for Forster resonance energy transfer. Our results showed tha t the constructed model system is promising as a starting point for in vestigations into the construction of biodevices for conversion of sol ar energy into electrical energy.