title: Spectroscopic properties of photosystem II core complexes from Thermosynechococcus elongatus revealed by single-molecule experiments.
abstract: In this study we use a combination of absorption, fluorescence and low temperature single-molecule spectroscopy to elucidate the spectral properties, heterogeneities and dynamics of the chlorophyll a (Chla) molecules responsible for the fluorescence emission of photosystem II core complexes (PS II cc) from the cyanobacterium Thermosynechococcus elongatus. At the ensemble level, the absorption and fluorescence spectra show a temperature dependence similar to plant PS II. We report emission spectra of single PS II cc for the first time; the spectra are dominated by zero-phonon lines (ZPLs) in the range between 680 and 705nm. The single-molecule experiments show unambiguously that different emitters and not only the lowest energy trap contribute to the low temperature emission spectrum. The average emission spectrum obtained from more than hundred single complexes shows three main contributions that are in good agreement with the reported bands F685, F689 and F695. The intensity of F695 is found to be lower than in conventional ensemble spectroscopy. The reason for the deviation might be due to the accumulation of triplet states on the red-most chlorophylls (e.g. Chl29 in CP47) or on carotenoids close to these long-wavelength traps by the high excitation power used in the single-molecule experiments. The red-most emitter will not contribute to the fluorescence spectrum as long as it is in the triplet state. In addition, quenching of fluorescence by the triplet state may lead to a decrease of long-wavelength emission.
authors: Universität Tübingen, IPTC and Lisa+ Center, Auf der Morgenstelle 18, Tübingen, Germany; Zurich University of Applied Sciences, Technikumstrasse 13, 8401 Winterthur, Switzerland. Electronic address: marc.brecht@uni-tuebingen.de.
authors: Marc
authors: M
authors: Brecht
authors: Universität Tübingen, IPTC and Lisa+ Center, Auf der Morgenstelle 18, Tübingen, Germany.
authors: Sepideh
authors: S
authors: Skandary
authors: Technische Universität Berlin, Max-Volmer-Institut, Straße des 17. Juni 135, Berlin, Germany.
authors: Julia
authors: J
authors: Hellmich
authors: Technische Universität Berlin, Max-Volmer-Institut, Straße des 17. Juni 135, Berlin, Germany.
authors: Carina
authors: C
authors: Glöckner
authors: Universität Tübingen, IPTC and Lisa+ Center, Auf der Morgenstelle 18, Tübingen, Germany.
authors: Alexander
authors: A
authors: Konrad
authors: Universität Tübingen, IPTC and Lisa+ Center, Auf der Morgenstelle 18, Tübingen, Germany.
authors: Martin
authors: M
authors: Hussels
authors: Universität Tübingen, IPTC and Lisa+ Center, Auf der Morgenstelle 18, Tübingen, Germany.
authors: Alfred J
authors: AJ
authors: Meixner
authors: Technische Universität Berlin, Max-Volmer-Institut, Straße des 17. Juni 135, Berlin, Germany; Humboldt Universität zu Berlin, Institut für Biologie, Philippstr. 13, 10099 Berlin, Germany.
authors: Athina
authors: A
authors: Zouni
authors: Technische Universität Berlin, Max-Volmer-Institut, Straße des 17. Juni 135, Berlin, Germany.
authors: Eberhard
authors: E
authors: Schlodder
mesh_terms: D019281:Dimerization; D008958:Models, Molecular; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D046940:Synechococcus / Q000737:chemistry*
chemical_list: D045332:Photosystem II Protein Complex
keywords: CP43; CP47; Fluorescence quenching; Low temperature spectroscopy; Photosystem II core complex; Single-molecule spectroscopy