Low light adaptation: energy transfer processes in different types of light harvesting complexes from Rhodopseudomonas palustris

Moulisova, V., Luer, L., Hoseinkhani, S., Brotosudarmo, T.H.P., Collins, A.M., Lanzani, G., Blankenship, R.E. and Cogdell, R.J. (2009) Low light adaptation: energy transfer processes in different types of light harvesting complexes from Rhodopseudomonas palustris. Biophysical Journal, 97(11), pp. 3019-3028. (doi:10.1016/j.bpj.2009.09.023)

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Abstract

Energy transfer processes in photosynthetic light harvesting 2 (LH2) complexes isolated from purple bacterium Rhodopseudomonas palustris grown at different light intensities were studied by ground state and transient absorption spectroscopy. The decomposition of ground state absorption spectra shows contributions from B800 and B850 bacteriochlorophyll (BChl) a rings, the latter component splitting into a low energy and a high energy band in samples grown under low light (LL) conditions. A spectral analysis reveals strong inhomogeneity of the B850 excitons in the LL samples that is well reproduced by an exponential-type distribution. Transient spectra show a bleach of both the low energy and high energy bands, together with the respective blue-shifted exciton-to-biexciton transitions. The different spectral evolutions were analyzed by a global fitting procedure. Energy transfer from B800 to B850 occurs in a mono-exponential process and the rate of this process is only slightly reduced in LL compared to high light samples. In LL samples, spectral relaxation of the B850 exciton follows strongly nonexponential kinetics that can be described by a reduction of the bleach of the high energy excitonic component and a red-shift of the low energetic one. We explain these spectral changes by picosecond exciton relaxation caused by a small coupling parameter of the excitonic splitting of the BChl a molecules to the surrounding bath. The splitting of exciton energy into two excitonic bands in LL complex is most probably caused by heterogenous composition of LH2 apoproteins that gives some of the BChls in the B850 ring B820-like site energies, and causes a disorder in LH2 structure.

Item Type:Articles
Additional Information:United States Department of Energy (DE- SC0001035), which established the Photosynthetic Antenna Research Center as a DOE Energy Frontier Research Center
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Moulisova, Dr Vladimira and Cogdell, Professor Richard and Brotosudarmo, Dr Tatas Hardo
Authors: Moulisova, V., Luer, L., Hoseinkhani, S., Brotosudarmo, T.H.P., Collins, A.M., Lanzani, G., Blankenship, R.E., and Cogdell, R.J.
Subjects:Q Science > QH Natural history > QH301 Biology
College/School:College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Biophysical Journal
ISSN:0006-3495
ISSN (Online):1542-0086
Published Online:26 November 2009

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