title: Generation of fluorescence quenchers from the triplet states of chlorophylls in the major light-harvesting complex II from green plants.
abstract: Laser flash-induced changes of the fluorescence yield were studied in aggregates of light-harvesting complex II (LHCII) on a time scale ranging from microseconds to seconds. Carotenoid (Car) and chlorophyll (Chl) triplet states, decaying with lifetimes of several microseconds and hundreds of microseconds, respectively, are responsible for initial light-induced fluorescence quenching via singlet-triplet annihilation. In addition, at times ranging from milliseconds to seconds, a slow decay of the light-induced fluorescence quenching can be observed, indicating the presence of additional quenchers generated by the laser. The generation of the quenchers is found to be sensitive to the presence of oxygen. It is proposed that long-lived fluorescence quenchers can be generated from Chl triplets that are not transferred to Car molecules. The quenchers could be Chl cations or other radicals that are produced directly from Chl triplets or via Chl triplet-sensitized singlet oxygen. Decay of the quenchers takes place on a millisecond to second time scale. The decay is slowed by a few orders of magnitude at 77 K indicating that structural changes or migration-limited processes are involved in the recovery. Fluorescence quenching is not observed for trimers, which is explained by a reduction of the quenching domain size compared to that of aggregates. This type of fluorescence quenching can operate under very high light intensities when Chl triplets start to accumulate in the light-harvesting antenna.
authors.affiliation: Faculty of Sciences, Division of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. vxb@chem.ucsd.edu
authors.forename: V
authors.initials: V
authors.lastname: Barzda
authors.forename: M
authors.initials: M
authors.lastname: Vengris
authors.forename: L
authors.initials: L
authors.lastname: Valkunas
authors.forename: R
authors.initials: R
authors.lastname: van Grondelle
authors.forename: H
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D002734:Chlorophyll / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D005453:Fluorescence; D007700:Kinetics; D007834:Lasers; D045342:Light-Harvesting Protein Complexes; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism; D018532:Pisum sativum / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; D010100:Oxygen