Abstract
The electronic structure of the circular aggregate of 18 bacteriochlorophyll a (BChl a) molecules responsible for the B850 absorption band of the light-harvesting 2 (LH2) complex of the photosynthetic purple bacterium Rhodopseudomonas acidophila has been studied by measuring fluorescence-excitation spectra of individual complexes at 1.2 K. The spectra reveal several well-resolved bands that are obscured in the single, broad B850 band observed in conventional absorption measurements on bulk samples. They are interpreted consistently in terms of the exciton model for the circular aggregate of BChl a molecules. From the energy separation between the different exciton transitions a reliable value of the intermolecular interaction is obtained. The spectra of the individual complexes allow for a distinction between the intra- and the intercomplex disorder. In addition to the random disorder, a regular modulation of the interaction has to be assumed to account for all the features of the observed spectra. This modulation has a C(2) symmetry, which strongly suggests a structural deformation of the ring into an ellipse.
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Selected References
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- Bopp M. A., Jia Y., Li L., Cogdell R. J., Hochstrasser R. M. Fluorescence and photobleaching dynamics of single light-harvesting complexes. Proc Natl Acad Sci U S A. 1997 Sep 30;94(20):10630–10635. doi: 10.1073/pnas.94.20.10630. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bopp M. A., Sytnik A., Howard T. D., Cogdell R. J., Hochstrasser R. M. The dynamics of structural deformations of immobilized single light-harvesting complexes. Proc Natl Acad Sci U S A. 1999 Sep 28;96(20):11271–11276. doi: 10.1073/pnas.96.20.11271. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Koolhaus M. H., Frese R. N., Fowler G. J., Bibby T. S., Georgakopoulou S., van der Zwan G., Hunter C. N., van Grondelle R. Identification of the upper exciton component of the B850 bacteriochlorophylls of the LH2 antenna complex, using a B800-free mutant of Rhodobacter sphaeroides. Biochemistry. 1998 Apr 7;37(14):4693–4698. doi: 10.1021/bi973036l. [DOI] [PubMed] [Google Scholar]
- Lösche M., Feher G., Okamura M. Y. The Stark effect in reaction centers from Rhodobacter sphaeroides R-26 and Rhodopseudomonas viridis. Proc Natl Acad Sci U S A. 1987 Nov;84(21):7537–7541. doi: 10.1073/pnas.84.21.7537. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Matsushita M., Ketelaars M., van Oijen A. M., Köhler J., Aartsma T. J., Schmidt J. Spectroscopy on the B850 band of individual light-harvesting 2 complexes of Rhodopseudomonas acidophila. II. Exciton states of an elliptically deformed ring aggregate. Biophys J. 2001 Mar;80(3):1604–1614. doi: 10.1016/S0006-3495(01)76133-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- van Oijen AM, Ketelaars M, Kohler J, Aartsma TJ, Schmidt J. Unraveling the electronic structure of individual photosynthetic pigment-protein complexes . Science. 1999 Jul 16;285(5426):400–402. doi: 10.1126/science.285.5426.400. [DOI] [PubMed] [Google Scholar]
- van Oijen A. M., Ketelaars M., Köhler J., Aartsma T. J., Schmidt J. Spectroscopy of individual light-harvesting 2 complexes of Rhodopseudomonas acidophila: diagonal disorder, intercomplex heterogeneity, spectral diffusion, and energy transfer in the B800 band. Biophys J. 2000 Mar;78(3):1570–1577. doi: 10.1016/S0006-3495(00)76709-9. [DOI] [PMC free article] [PubMed] [Google Scholar]