title: Carotenoid charge transfer states and their role in energy transfer processes in LH1-RC complexes from aerobic anoxygenic phototrophs.
abstract: Light-harvesting complexes ensure necessary flow of excitation energy into photosynthetic reaction centers. In the present work, transient absorption measurements were performed on LH1-RC complexes isolated from two aerobic anoxygenic phototrophs (AAPs), Roseobacter sp. COL2P containing the carotenoid spheroidenone, and Erythrobacter sp. NAP1 which contains the carotenoids zeaxanthin and bacteriorubixanthinal. We show that the spectroscopic data from the LH1-RC complex of Roseobacter sp. COL2P are very similar to those previously reported for Rhodobacter sphaeroides, including the transient absorption spectrum originating from the intramolecular charge-transfer (ICT) state of spheroidenone. Although the ICT state is also populated in LH1-RC complexes of Erythrobacter sp. NAP1, its appearance is probably related to the polarity of the bacteriorubixanthinal environment rather than to the specific configuration of the carotenoid, which we hypothesize is responsible for populating the ICT state of spheroidenone in LH1-RC of Roseobacter sp. COL2P. The population of the ICT state enables efficient S1/ICT-to-bacteriochlorophyll (BChl) energy transfer which would otherwise be largely inhibited for spheroidenone and bacteriorubixanthinal due to their low energy S1 states. In addition, the triplet states of these carotenoids appear well-tuned for efficient quenching of singlet oxygen or BChl-a triplets, which is of vital importance for oxygen-dependent organisms such as AAPs.
authors.affiliation: Faculty of Science, University of South Bohemia , Branišovská 31, 370 05 České Budějovice, Czech Republic.
authors.forename: Václav
authors.initials: V
authors.lastname: Šlouf
authors.forename: Marcel
authors.initials: M
authors.lastname: Fuciman
authors.forename: Alexander
authors.initials: A
authors.lastname: Dulebo
authors.forename: David
authors.initials: D
authors.lastname: Kaftan
authors.forename: Michal
authors.initials: M
authors.lastname: Koblížek
authors.forename: Harry A
authors.initials: HA
authors.lastname: Frank
authors.forename: Tomáš
authors.initials: T
authors.lastname: Polívka
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001429:Bacteriochlorophylls / Q000737:chemistry; D002338:Carotenoids / Q000737:chemistry*; D004735:Energy Transfer; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000378:metabolism; D041904:Roseobacter / Q000378:metabolism*; D042301:Sphingomonadaceae / Q000378:metabolism; D024341:Xanthophylls / Q000737:chemistry*; D065146:Zeaxanthins
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D024341:Xanthophylls; D065146:Zeaxanthins; C104880:spheroidenone; D002338:Carotenoids