Tönu Pullerits
Professor
B800→B850 energy transfer mechanism in bacterial LH2 complexes investigated by B800 pigment exchange
Author
Summary, in English
Femtosecond transient absorption measurements were performed on native and a series of reconstituted LH2 complexes from Rhodopseudomonas acidophila
10050 at room temperature. The reconstituted complexes contain
chemically modified tetrapyrrole pigments in place of the native
bacteriochlorophyll a-B800 molecules. The spectral
characteristics of the modified pigments vary significantly, such that
within the B800 binding sites the B800 Qy absorption maximum can be shifted incrementally from 800 to 670 nm. As the spectral overlap between the B800 and B850 Qy
bands decreases, the rate of energy transfer (as determined by the
time-dependent bleaching of the B850 absorption band) also decreases;
the measured time constants range from 0.9 ps (bacteriochlorophyll a in the B800 sites, Qy absorption maximum at 800 nm) to 8.3 ps (chlorophyll a in the B800 sites, Qy absorption maximum at 670 nm).
This correlation between energy transfer rate and spectral blue-shift
of the B800 absorption band is in qualitative agreement with the trend
predicted from Förster spectral overlap calculations, although the
experimentally determined rates are ∼5 times faster than those predicted
by simulations. This discrepancy is attributed to an underestimation of
the electronic coupling between the B800 and B850 molecules.
10050 at room temperature. The reconstituted complexes contain
chemically modified tetrapyrrole pigments in place of the native
bacteriochlorophyll a-B800 molecules. The spectral
characteristics of the modified pigments vary significantly, such that
within the B800 binding sites the B800 Qy absorption maximum can be shifted incrementally from 800 to 670 nm. As the spectral overlap between the B800 and B850 Qy
bands decreases, the rate of energy transfer (as determined by the
time-dependent bleaching of the B850 absorption band) also decreases;
the measured time constants range from 0.9 ps (bacteriochlorophyll a in the B800 sites, Qy absorption maximum at 800 nm) to 8.3 ps (chlorophyll a in the B800 sites, Qy absorption maximum at 670 nm).
This correlation between energy transfer rate and spectral blue-shift
of the B800 absorption band is in qualitative agreement with the trend
predicted from Förster spectral overlap calculations, although the
experimentally determined rates are ∼5 times faster than those predicted
by simulations. This discrepancy is attributed to an underestimation of
the electronic coupling between the B800 and B850 molecules.
Department/s
- Chemical Physics
Publishing year
2000
Language
English
Pages
2590-2596
Publication/Series
Biophysical Journal
Volume
78
Issue
5
Document type
Journal article
Publisher
Cell Press
Topic
- Biophysics
Status
Published
ISBN/ISSN/Other
- ISSN: 0006-3495