title: The efficiency of non-photochemical fluorescence quenching by cation radicals in photosystem II reaction centers.
abstract: In a direct experiment, the rate constants of photochemical kpand non-photochemical kp+quenching of the chlorophyll fluorescence have been determined in spinach photosystem II (PS II) membrane fragments, oxygen-evolving PS II core, as well as manganese-depleted PS II particles using pulse fluorimetry. In the dark-adapted reaction center(s) (RC), the fluorescence decay kinetics of the antenna were measured at low-intensity picosecond pulsed excitation. To create a "closed" P680+QA-state, RCs were illuminated by high-intensity actinic flash 8 ns prior to the measuring flash. The obtained data were approximated by the sum of two decaying exponents. It was found that the antennae fluorescence quenching efficiency by the oxidized photoactive pigment of RC P680+was about 1.5 times higher than that of the neutral P680 state. These results were confirmed by a single-photon counting technique, which allowed to resolve the additional slow component of the fluorescence decay. Slow component was assigned to the charge recombination of P680+Pheo-in PS II RC. Thus, for the first time, the ratio kp+/kp≅ 1.5 was found directly. The mechanism of the higher efficiency of non-photochemical quenching comparing to photochemical quenching is discussed.
authors.affiliation: Biophysical Department, Faculty of Biology, M.V.Lomonosov Moscow State University, Leninskye Gory 1, Build. 12, Moscow, Russia, 119234. vz.paschenko@gmail.com.
authors.forename: V Z
authors.identifier: http://orcid.org/0000-0002-0921-5513
authors.initials: VZ
authors.lastname: Paschenko
authors.affiliation: Biophysical Department, Faculty of Biology, M.V.Lomonosov Moscow State University, Leninskye Gory 1, Build. 12, Moscow, Russia, 119234.
authors.forename: A A
authors.initials: AA
authors.lastname: Churin
authors.affiliation: Biophysical Department, Faculty of Biology, M.V.Lomonosov Moscow State University, Leninskye Gory 1, Build. 12, Moscow, Russia, 119234.
authors.forename: V V
authors.initials: VV
authors.lastname: Gorokhov
authors.affiliation: Biophysical Department, Faculty of Biology, M.V.Lomonosov Moscow State University, Leninskye Gory 1, Build. 12, Moscow, Russia, 119234.
authors.forename: N P
authors.initials: NP
authors.lastname: Grishanova
authors.affiliation: Biophysical Department, Faculty of Biology, M.V.Lomonosov Moscow State University, Leninskye Gory 1, Build. 12, Moscow, Russia, 119234.
authors.forename: B N
authors.initials: BN
authors.lastname: Korvatovskii
authors.affiliation: Biophysical Department, Faculty of Biology, M.V.Lomonosov Moscow State University, Leninskye Gory 1, Build. 12, Moscow, Russia, 119234.
authors.forename: E G
authors.initials: EG
authors.lastname: Maksimov
authors.affiliation: A.N.Belozersky Institute of Physico-Chemical Biology, Moscow State University, Leninskye Gory 1, Build. 40, Moscow, Russia, 119992.
authors.forename: M D
authors.initials: MD
authors.lastname: Mamedov
mesh_terms: D002412:Cations / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D005453:Fluorescence; D005609:Free Radicals / Q000378:metabolism; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018724:Spinacia oleracea / Q000378:metabolism
chemical_list: D002412:Cations; D005609:Free Radicals; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D010100:Oxygen
keywords: Light-harvesting antenna; Non-photochemical quenching; Photochemical reactions; Photosystem II; Reaction center