Tracking energy transfer between light harvesting complex 2 and 1 in photosynthetic membranes grown under high and low illumination

Luer, L., Moulisova, V. , Henry, S., Polli, D., Brotosudarmo, T.H.P., Hoseinkhani, S., Brida, D., Lanzani, G., Cerullo, G. and Cogdell, R.J. (2012) Tracking energy transfer between light harvesting complex 2 and 1 in photosynthetic membranes grown under high and low illumination. Proceedings of the National Academy of Sciences of the United States of America, 109(5), pp. 1473-1478. (doi:10.1073/pnas.1113080109)

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Abstract

Energy transfer (ET) between B850 and B875 molecules in light harvesting complexes LH2 and LH1/RC (reaction center) complexes has been investigated in membranes of Rhodopseudomonas palustris grown under high- and low-light conditions. In these bacteria, illumination intensity during growth strongly affects the type of LH2 complexes synthesized, their optical spectra, and their amount of energetic disorder. We used a specially built femtosecond spectrometer, combining tunable narrowband pump with broadband white-light probe pulses, together with an analytical method based on derivative spectroscopy for disentangling the congested transient absorption spectra of LH1 and LH2 complexes. This procedure allows real-time tracking of the forward (LH2 → LH1) and backward (LH2←LH1) ET processes and unambiguous determination of the corresponding rate constants. In low-light grown samples, we measured lower ET rates in both directions with respect to high-light ones, which is explained by reduced spectral overlap between B850 and B875 due to partial redistribution of oscillator strength into a higher energetic exciton transition. We find that the low-light adaptation in R. palustris leads to a reduced elementary backward ET rate, in accordance with the low probability of two simultaneous excitations reaching the same LH1/RC complex under weak illumination. Our study suggests that backward ET is not just an inevitable consequence of vectorial ET with small energetic offsets, but is in fact actively managed by photosynthetic bacteria.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Henry, Dr Sarah and Moulisova, Dr Vladimira and Cogdell, Professor Richard and Brotosudarmo, Dr Tatas Hardo
Authors: Luer, L., Moulisova, V., Henry, S., Polli, D., Brotosudarmo, T.H.P., Hoseinkhani, S., Brida, D., Lanzani, G., Cerullo, G., and Cogdell, R.J.
College/School:College of Medical Veterinary and Life Sciences > Institute of Cancer Sciences
College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Proceedings of the National Academy of Sciences of the United States of America
Journal Abbr.:Proc. Natl. Acad. Sci.
Publisher:National Academy of Sciences
ISSN:0027-8424
ISSN (Online):1091-6490
Published Online:23 January 2012

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