Optically detected magnetic resonance of intact membranes from Chloroflexus aurantiacus. Evidence for exciton interaction between the RC and the B808–866 complex |
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Authors: | Bordignon Enrica Scarzello Marco Agostini Giancarlo Giacometti Giovanni Vianelli Alberto Vannini Candida Carbonera Donatella |
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Institution: | (1) Department of Physical Chemistry, University of Padova, via Loredan 2, 35131, Padova, Italy;(2) Centro Studi Stati Molecolari Radicalici ed Eccitati CNR, via Loredan 2, 35131, Padova, Italy;(3) Department of Structural and Functional Biology, University of Insubria, via J.H. Dunant 3, 21100, Varese, Italy |
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Abstract: | Optically detected magnetic resonance of chlorosome-containing membranes from the green filamentous bacterium Chloroflexus aurantiacus has been performed both by fluorescence and absorption detection. Triplet states localized in the chlorosomes and in the B808–866 complex have been characterized. After chemical reduction with ascorbate followed by illumination at 200 K, recombination triplet state localized in the primary donor becomes largely populated under illumination at low temperature while all the antenna triplet states, which are localized in carotenoids and BChl a molecules, are strongly quenched. We were able to obtain the T-S spectrum of the primary donor P870 surrounded by all the antenna complexes connected to the RC via energy transfer and then in its intact environment. We found clear spectroscopic evidence for exciton interaction between the RC and the B808–866 antenna complex. This evidence was provided by the comparison of the T–S spectrum of P870 in the membranes with that of isolated RC. The analogy of some features of the difference spectra with those previously found in the same kind of experiments for Rb. sphaeroides, allows to predict a similar coupling among the primary donor and the nearby antenna BChl a molecules, assembled as circular aggregate.This revised version was published online in October 2005 with corrections to the Cover Date. |
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Keywords: | ADMR bacteriochlorophyll B808– 866 carotenoid chlorosomes FDMR Reaction center triplet state T– S |
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