Fluorescence-excitation and Emission Spectroscopy on Single FMO Complexes

In green-sulfur bacteria sunlight is absorbed by antenna structures termed chlorosomes, and transferred to the RC via the Fenna-Matthews-Olson (FMO) complex. FMO consists of three monomers arranged in C3 symmetry where each monomer accommodates eight Bacteriochlorophyll a (BChl a) molecules. It was the first pigment-protein complex for which the structure has been determined with high resolution and since then this complex has been the subject of numerous studies both experimentally and theoretically. Here we report about fluorescence-excitation spectroscopy as well as emission spectroscopy from individual FMO complexes at low temperatures. The individual FMO complexes are subjected to very fast spectral fluctuations smearing out any possible different information from the ensemble data that were recorded under the same experimental conditions. In other words, on the time scales that are experimentally accessible by single-molecule techniques, the FMO complex exhibits ergodic behaviour.