Picosecond absorbance difference spectra of the antenna of photosynthetic purple bacteria The influence of exciton interactions and librations

As the electronic energies of the chromophores in a pigment–protein complex are imposed by the geometrical structure of the protein, this allows the spectral information obtained to be compared with predictions derived from structural models. Thereby, the single-molecule approach is particularly suited for the elucidation of specific, distinctive spectral features that are key for a particular model structure, and that would not be observable in ensemble-averaged spectra due to the heterogeneity of the biological objects. In this concise review, we illustrate with the example of the light-harvesting complexes from photosynthetic purple bacteria how results from low-temperature single-molecule spectroscopy can be used to discriminate between different structural models. Thereby the low-temperature approach provides two advantages: (i) owing to the negligible photobleaching, very long observation times become possible, and more importantly, (ii) at cryogenic temperatures, vibrational degrees of freedom are frozen out, leading to sharper spectral features and in turn to better resolved spectra.

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Ultrafast Energy Transfer Within the Light-Harvesting Antenna of Photosynthetic Purple Bacteria

Ultrafast Phenomena VIII - Springer Series in Chemical Physics ◽

10.1007/978-3-642-84910-7_180 ◽

1993 ◽

pp. 559-561 ◽

Cited By ~ 2

Author(s):

K. J. Visscher ◽

V. Gulbinas ◽

R. J. Cogdell ◽

R. van Grondelle ◽

V. Sundström

Keyword(s):

Energy Transfer ◽

Light Harvesting ◽

Purple Bacteria ◽

Photosynthetic Purple Bacteria ◽

Light Harvesting Antenna

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Light-Induced Oxidation-Reduction Reactions of Photosystem II in Dichlorophenyl-dimethyl Urea (DCM U) Inhibited Thylakoids

Zeitschrift für Naturforschung C ◽

10.1515/znc-1990-3-420 ◽

1990 ◽

Vol 45 (3-4) ◽

pp. 258-264

Author(s):

Jeff A. Nemson ◽

Anastasios Melis

Keyword(s):

Difference Spectrum ◽

Thylakoid Membranes ◽

Donor Side ◽

Difference Spectra ◽

Ps Ii ◽

Oxidation Reduction ◽

Primary Quinone Acceptor ◽

Dimethyl Urea ◽

Absorbance Difference ◽

Quinone Acceptor

Abstract Illumination of thylakoid membranes in the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethyl urea (DCMU) causes the reduction of the primary quinone acceptor QA of photosystem II (PS II) and the storage of a positive charge on the donor side of the photochemical reaction center. These oxidation-reduction reactions are accompanied by characteristic changes of absorbance in the ultra-violet region of the spectrum. The PS II-related absorbance difference spectra (250 -350 nm) were compared in control and hydroxylamine-treated thylakoid membranes, and in thylakoids suspended in the presence of carbonyl cyanide-p-(trifluoromethoxy)- phenylhydrazone (FCCP). The light minus dark difference spectra were dominated by the Q-A minus QA difference spectrum. Qualitatively, the three spectra were identical in the 300 - 350 nm region, however, they showed distinct differences in the 250 - 300 nm region. The latter arose because of different contributions from the donor side of PS II in the thylakoid membrane of the three samples. The result suggested that FCCP acts as the ultimate electron donor in DCMU - poisoned chloroplasts. Therefore, the absorbance difference spectrum in the presence of FCCP reflected a contribution from the Q-A minus QA component only. Deconvolution of the absorbance difference spectra of control and hydroxylamine-treated thylakoids yielded difference spectra attributed to the oxidation of a component on the donor side of PS II. This component did not conform with the known Mn(III) → Mn(IV) transition. Rather, it indicated the oxidation of a modified form of Mn in the presence of DCMU , probably a Mn(II) → Mn(III) transition. The results are discussed in terms of the use of DCMU - poisoned thylakoid membranes in the quantitation of the primary quinone acceptor QA by spectrophotometric approaches.

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