Fluorescence and Photobleaching Dynamics of Single Light-Harvesting Complexes

Single light-harvesting complexes LH-2 from Rhodopseudomonas acidophila were immobilized on various charged surfaces under physiological conditions. Polarized light experiments showed that the complexes were situated on the surface as nearly upright cylinders. Their fluorescence lifetimes and photob...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1997-09, Vol.94 (20), p.10630-10635
Main Authors: Bopp, Martin A., Jia, Yiwei, Li, Liangquan, Cogdell, Richard J., Hochstrasser, Robin M.
Format: Article
Language:English
Subjects:
Biochemistry
Biological Sciences
Bleaching
Carotenoids
Cylinders
Energy transfer
Fluorescence
Fluorescence Polarization
Light
Light-Harvesting Protein Complexes
Luminous intensity
Mica
Microscopes
Microscopy, Confocal
Molecular excitation
Molecules
Photosynthetic Reaction Center Complex Proteins - chemistry
Physics
Rhodopseudomonas - chemistry
Time
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Summary:Single light-harvesting complexes LH-2 from Rhodopseudomonas acidophila were immobilized on various charged surfaces under physiological conditions. Polarized light experiments showed that the complexes were situated on the surface as nearly upright cylinders. Their fluorescence lifetimes and photobleaching properties were obtained by using a confocal fluorescence microscope with picosecond time resolution. Initially all molecules fluoresced with a lifetime of 1 ± 0.2 ns, similar to the bulk value. The photobleaching of one bacteriochlorophyll molecule from the 18-member assembly caused the fluorescence to switch off completely, because of trapping of the mobile excitations by energy transfer. This process was linear in light intensity. On continued irradiation the fluorescence often reappeared, but all molecules did not show the same behavior. Some LH-2 complexes displayed a variation of their quantum yields that was attributed to photoinduced confinement of the excited states and thereby a diminution of the superradiance. Others showed much shorter lifetimes caused by excitation energy traps that are only ≈ 3% efficient. On repeated excitation some molecules entered a noisy state where the fluorescence switched on and off with a correlation time of ≈ 0.1 s. About 490 molecules were examined.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.94.20.10630