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Allophycocyanin and energy transfer.
1Wadsworth Center, Laboratories and Research, New York State Department of Health, P.O. Box 509, Albany, NY 12201-0509 USA. robert.maccoll@wadsworth.org
Biochimica Et Biophysica Acta
|July 9, 2004
Summary
Allophycocyanin trimers exhibit an unusual 650 nm absorption peak. Sophisticated biophysical methods suggest strong exciton coupling between chromophores, rather than protein environment interactions, explains this red shift.
Area of Science:
- Biophysics
- Photochemistry
- Spectroscopy
Background:
- Allophycocyanin is a biliprotein found in phycobilisomes, functioning as a light-harvesting component.
- It exists as a trimer (alpha3beta3) or monomer (alphabeta), with each subunit containing a phycocyanobilin chromophore.
- The trimer displays an anomalous absorption maximum at 650 nm, distinct from the monomer's 615 nm maximum.
Purpose of the Study:
- To investigate the cause of the 650 nm absorption maximum in allophycocyanin trimers.
- To differentiate between two proposed models: local protein environment interactions versus exciton coupling.
Main Methods:
- Utilized a variety of biophysical techniques.
- Employed sophisticated ultra-fast fluorescence spectroscopy.
Main Results:
- Evidence supporting both proposed models was initially observed.
- Ultra-fast fluorescence data strongly favors the exciton coupling hypothesis.
- Exciton coupling between chromophores across monomer-monomer interfaces leads to absorption red shift.
Conclusions:
- Strong exciton coupling between chromophore pairs within allophycocyanin trimers is the most likely explanation for the 650 nm absorption maximum.
- Förster resonance energy transfer (FRET) is proposed to occur between these strongly coupled pairs.
- Monomers exhibit FRET between their two chromophores.