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Biophys. J. BioFAST: First Published March 24, 2006. doi:10.1529/biophysj.105.076612
© 2006 by the Biophysical Society.

A more recent version of this article appeared on June 1, 2006.
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PHOTOBIOPHYSICS

Ultrafast Carotenoid-to-Chlorophyll Singlet Energy Transfer in the Cytochrome b6f complex from Bryopsis corticulans

Ping Zuo 1, Bin-Xing Li 2, Xiao-Hui Zhao 1, Yi-Shi Wu 1, Xi-Cheng Ai 1, Jian-Ping Zhang 1*, Liang-Bi Li 2 and Ting-Yun Kuang 2

1 Institute of Chemistry, Chinese Academy of Sciences
2 Institute of Botany, Chinese Academy of Sciences

* To whom correspondence should be addressed. E-mail: jpzhang{at}mail.iccas.ac.cn.

Submitted on October 25, 2005
Revised on December 6, 2005
Accepted on 3 March 2006


  Abstract
Ultrafast carotenoid-to-chlorophyll (Car-to-Chl) singlet excitation energy transfer in the cytochrome b6f (Cyt b6f) complex from Bryopsis corticulans is investigated by the use of femtosecond time-resolved absorption spectroscopy. For all-trans-{alpha}-carotene free in n-hexane, the lifetimes of the two low-lying singlet excited states, S1(2Ag-) and S2(1Bu+), are determined to be 14.3 ± 0.4 ps and 230 ± 10 fs, respectively. For the Cyt b6f complex, to which 9-cis-{alpha}-carotene is bounded, the lifetime of S1(2Ag-) state remains unchanged, while that of the S2(1Bu+) state is significantly reduced. In addition, a decay-to-rise correlation between the excited state dynamics of {alpha}-carotene and Chl a is clearly observed. These spectroscopic evidence prove that the S2(1Bu+) state is able to transfer electronic excitations to the Qx state of Chl a, whereas the S1(2Ag-) state remains inactive. The time constant and the partial efficiency of the energy transfer are determined to be 240 ± 40 fs and (49 ± 4)%, respectively, which supports the overall efficiency of 24% determined with steady state fluorescence spectroscopy. A scheme of the {alpha}-carotene-to-Chl a singlet energy transfer is proposed based on the excited-state dynamics of the pigments.

Key Words: Bryopsis corticulans, Cytochrome b6f complex, alpha-carotene, chlorophyll, energy transfer, time-resolved spectroscopy




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Site-Specific Solvation of the Photoexcited Protochlorophyllide a in Methanol: Formation of the Hydrogen-Bonded Intermediate State Induced by Hydrogen-Bond Strengthening
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Copyright © 2006 by the Biophysical Society.