Excitation energy transfer in chlorosomes of Chlorobium phaeobacteroides strain CL1401: the role of carotenoids |
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Authors: | Pšenčík Jakub Ma Ying-Zhong Arellano Juan B. Garcia-Gil Jesús Holzwarth Alfred R. Gillbro Tomas |
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Affiliation: | (1) Department of Chemistry, Biophysical Chemistry, Umeå University, S-901 87 Umeå, Sweden;(2) Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic;(3) Max-Planck-Institut für Strahlenchemie, Stiftstr. 34-36, D-45470 Mülheim a.d. Ruhr, Germany;(4) Present address: Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA;(5) Laboratory of Microbiology, Institute of Aquatic Ecology, University of Girona, Campus de Montilivi, Girona, Spain;(6) Present address: Instituto de Recursos Naturales y Agrobiologia (CSIC), Cordel de Merinas 52, 37008 Salamanca, Spain |
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Abstract: | The role of carotenoids in chlorosomes of the green sulfur bacterium Chlorobium phaeobacteroides, containing bacteriochlorophyll (BChl) e and the carotenoid (Car) isorenieratene as main pigments, was studied by steady-state fluorescence excitation, picosecond single-photon timing and femtosecond transient absorption (TA) spectroscopy. In order to obtain information about energy transfer from Cars in this photosynthetic light-harvesting antenna with high spectral overlap between Cars and BChls, Car-depleted chlorosomes, obtained by inhibition of Car biosynthesis by 2-hydroxybiphenyl, were employed in a comparative study with control chlorosomes. Excitation spectra measured at room temperature give an efficiency of 60–70% for the excitation energy transfer from Cars to BChls in control chlorosomes. Femtosecond TA measurements enabled an identification of the excited state absorption band of Cars and the lifetime of their S1 state was determined to be 10 ps. Based on this lifetime, we concluded that the involvement of this state in energy transfer is unlikely. Furthermore, evidence was obtained for the presence of an ultrafast (>100 fs) energy transfer process from the S2 state of Cars to BChls in control chlorosomes. Using two time-resolved techniques, we further found that the absence of Cars leads to overall slower decay kinetics probed within the Qy band of BChl e aggregates, and that two time constants are generally required to describe energy transfer from aggregated BChl e to baseplate BChl a.This revised version was published online in October 2005 with corrections to the Cover Date. |
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Keywords: | bacteriochlorophyll carotenoid chlorosome Chlorobiaceae energy transfer femtosecond spectroscopy fluorescence excitation green sulfur bacteria single-photon timing |
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