On the Controversial Nature of the 825 nm Exciton Band in the FMO Protein Complex.
The nature of the low-energy 825 nm band of the Fenna-Matthews-Olson (FMO) protein complex from Chlorobaculum tepidum at 5 K is discussed. It is shown, using hole-burning (HB) spectroscopy and excitonic calculations, that the 825 nm absorption band of the FMO trimer cannot be explained by a single electronic transition or overlap of electronic transitions of noninteracting pigments. To explain the shape of emission and nonresonant HB spectra, downward uncorrelated excitation energy transfer (EET) between trimer subunits should be taken into account. Modeling studies reveal the presence of three sub-bands within the 825 nm band, in agreement with nonresonant HB and emission spectra. We argue that after light induced coherences vanish, uncorrelated EET between the lowest exciton levels of each monomer takes place. HB induced spectral shifts provide a new insight on the energy landscape of the FMO protein.
Adam
A
Kell
Khem
K
Acharya
§Department of Physics, Concordia University, Montreal H4B 1R6, Quebec, Canada.
Valter
V
Zazubovich
Ryszard
R
Jankowiak
Fenna−Matthews−Olson; bacteriochlorophyll; energy transfer; photosynthesis