Electrostatic effect of surfactant molecules on bacteriochlorophyll a and carotenoid binding sites in the LH1 complex isolated from Rhodospirillum rubrum S1 probed by Stark spectroscopy |
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Authors: | Katsunori Nakagawa Satoru Suzuki Ritsuko Fujii Alastair T Gardiner Richard J Cogdell Mamoru Nango Hideki Hashimoto |
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Institution: | (1) Department of Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Nagoya 466-8555, Japan;(2) Department of Physics, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan;(3) Glasgow Biomedical Research Centre, Institute of Biomedical and Life Sciences, University of Glasgow, 120 University Place, Glasgow, 8QQ, Scotland, UK |
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Abstract: | The LH1 complexes were isolated from the purple photosynthetic bacterium Rhodospirillum rubrum strain S1. They were initially solubilized using LDAO and then purified in the presence of Triton X-100. The purified complexes
were then either used directly or following an exchange into LDAO. Stark spectroscopy was applied to probe the electrostatic
field around the bacteriochlorophyll a (BChl a) and carotenoid binding sites in the LH1 complexes surrounded by these two different surfactant molecules. Polarizabilty
change
() and dipole moment change () upon photoexcitation were determined for the BChl a Qy band. Both of these parameters show smaller values in the presence of LDAO than in Triton X-100. This indicates that polar
detergent molecules, like LDAO, affect the electrostatic environment around BChl a, and modify the nonlinear optical parameters ( and values). The electrostatic field around the BChl a binding site, which is generated by the presence of LDAO, was determined to be |E
L
| = ∼3.9 × 105 V/cm]. Interestingly, this kind of electrostatic effect was not observed for the carotenoid-binding site. The present study
demonstrates a unique electrostatic interaction between the polar detergent molecules surrounding the LH1 complex and the
Qy absorption band of BChl a that is bound to the LH1 complex. |
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Keywords: | Bacteriochlorophyll Carotenoid LH1 complex Non-polar detergent Polar detergent Purple photosynthetic bacteria Stark spectroscopy |
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