Combined fluorescence and photovoltage studies on chlorosome containing bacteria - II. Whole cells and chlorosome-depleted membranes of Chlorobium limicola

Autor(en): Schmidt, KA
Trissl, HW
Stichwörter: BACTERIOCHLOROPHYLL-C; charge stabilization; CHLOROFLEXUS-AURANTIACUS; energy transfer; ENERGY-TRANSFER; EXCITED-STATES; fluorescence quenching; FMO-protein; GREEN SULFUR BACTERIA; green sulfur bacterium; PHOTOSYNTHETIC REACTION-CENTER; PHOTOSYSTEM-I; Plant Sciences; PRIMARY CHARGE SEPARATION; PRIMARY ELECTRON-ACCEPTOR; PROSTHECOCHLORIS-AESTUARII; trapping
Erscheinungsdatum: 1998
Herausgeber: KLUWER ACADEMIC PUBL
Journal: PHOTOSYNTHESIS RESEARCH
Volumen: 58
Ausgabe: 1
Startseite: 57
Seitenende: 70
Zusammenfassung: 
Energy transfer kinetics and primary charge separation were studied in whole cells and in chlorosome-depleted membranes of Chlorobium limicola by ps-fluorescence and ps-photovoltage as well as by stationary fluorescence spectroscopy. The fluorescence decay kinetics of whole cells indicate a sequential energy transfer from the chlorosomes via the baseplates and the Fenna-Matthews-Olson-protein (FMO) to the core-complexes with time constants of 35 /- 4 ps and 95 /- 10 ps, respectively. The quantitative analysis of fluorescence spectra and the occurrence of slow phases in the fluorescence decays reveal that in whole cells a significant fraction of BChl c in the chlorosome and of BChl a in the baseplate-FMO-protein is poorly connected to the core-complexes. The photovoltage kinetics of whole cells upon excitation in the chlorosome (lambda(ex) = 532 nm) consisted of two electrogenic phases with time constants of 121 /- 10 ps and 575 /- 140 ps. The approximate to 120 ps phase is composed of energy transfer from the baseplate-FMO-protein to the core-complex and trapping from the core-complexes by P(+)A(0)(-) formation. The second phase (relative electrogenicity of 23%) is a charge stabilization step, probably from the first electron acceptor, A(0), to the secondary electron acceptor F-X. When the core-complexes were excited (lambda(ex) = 840 nm) the photovoltage kinetics also consisted of two electrogenic phases, but the first phase showed a time constant of 23 /- 6 ps. This phase reflects exclusively trapping from the core-complexes by P(+)A(0)(-) formation. In dark-adapted whole cells the fluorescence yields of the peripheral antenna complexes increased strongly upon background illumination. This observation indicates the disappearance of endogenous quenchers, probably quinones.
ISSN: 01668595
DOI: 10.1023/A:1006093627724

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