Excitation energy flow in chlorosome antennas of green photosynthetic bacteria
- National Institute for Basic Biology, Aichi (Japan)
- Tohoku Univ., Miyagi (Japan)
- Institute for Molecular Science, Aichi (Japan)
- Tokyo Metropolitan Univ. (Japan)
- Univ. of Rochester, NY (USA)
- Arizona State Univ., Tempe (USA)
Energy flow in whole cells of the thermophilic green photosynthetic bacterium Chloroflexus aurantiacus was studied by measurements of time-resolved fluorescence spectra in the picosecond time range, detected by both streak camera and single-photon counting methods. These data characterize the energy-transfer sequence from bacteriochlorophyll c (BChl c), found in membrane-associated antenna structures called chlorosomes, to BChl a in the chlorosome baseplate, then to a BChl a antenna complex in the cytoplasmic membrane, and finally to the photochemical reaction center. Upon selective excitation of BChl c in chlorosomes, the decay time of the emission arising from BChl c was 16 ps. The apparent rise time of the emission from the baseplate pigment was < 3 ps. The time course of the transfer from the baseplate BChl a to the membrane-bound BChl a complex was clearly detected. A major 41-ps decay component of the baseplate BChl a emission corresponded to the rise term found for the membrane-bound BChl a emission. With a kinetic analysis, a model is proposed for the structure and function of the chlorosome antenna system in Chloroflexus aurantiacus. The data suggest that the excitation-transfer process may utilize a novel mechanism that takes advantage of the photophysical properties of aggregated pigments. BChl c molecules form naturally occurring aggregates with oligomeric structures similar to J aggregates, but very different from the organization of antenna pigment-proteins from other photosynthetic organisms. These oligomers absorb light and transfer excitations to a small amount of BChl a antenna proteins in the baseplate. The baseplate acts as an energy-transfer interface between the chlorosome and the antenna protein complexes located within the membrane. The integral membrane antenna complexes in turn deliver the excitations to the reaction center where photosynthesis is initiated by electron-transfer reactions.
- OSTI ID:
- 6823386
- Journal Information:
- Journal of Physical Chemistry; (USA), Vol. 93:21; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
14 SOLAR ENERGY
PHOTOSYNTHETIC BACTERIA
ENERGY TRANSPORT
DATA ANALYSIS
EXPERIMENTAL DATA
FLUORESCENCE SPECTROSCOPY
MEASURING INSTRUMENTS
MEASURING METHODS
PHOTOSYNTHESIS
CHEMICAL REACTIONS
DATA
EMISSION SPECTROSCOPY
INFORMATION
NUMERICAL DATA
PHOTOCHEMICAL REACTIONS
SPECTROSCOPY
SYNTHESIS
400201* - Chemical & Physicochemical Properties
140505 - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)