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Biochim Biophys Acta. 2014 Jun;1837(6):773-81. doi: 10.1016/j.bbabio.2014.01.025. Epub 2014 Feb 6.

Spectroscopic properties of photosystem II core complexes from Thermosynechococcus elongatus revealed by single-molecule experiments.

Author information

1
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.
2
Universität Tübingen, IPTC and Lisa+ Center, Auf der Morgenstelle 18, Tübingen, Germany.
3
Technische Universität Berlin, Max-Volmer-Institut, Straße des 17. Juni 135, Berlin, Germany.
4
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.

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.

KEYWORDS:

CP43; CP47; Fluorescence quenching; Low temperature spectroscopy; Photosystem II core complex; Single-molecule spectroscopy

PMID:
24508723
DOI:
10.1016/j.bbabio.2014.01.025
[Indexed for MEDLINE]
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