Local electrostatic field induced by the carotenoid bound to the reaction center of the purple photosynthetic bacterium Rhodobacter sphaeroides

Yanagi, K., Shimizu, M., Hashimoto, H., Gardiner, A.T., Roszak, A.W. and Cogdell, R.J. (2005) Local electrostatic field induced by the carotenoid bound to the reaction center of the purple photosynthetic bacterium Rhodobacter sphaeroides. Journal of Physical Chemistry B, 109(2), pp. 992-998. (doi:10.1021/jp046929d)

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Abstract

Electroabsorption (EA) spectra were recorded in the region of the reaction center (RC) Qy absorption bands of bacteriochlorophyll (Bchl) and bacteriopheophytin, to investigate the effect of carotenoid (Car) on the electrostatic environment of the RCs of the purple bacterium Rhodobacter (Rb.) sphaeroides. Two different RCs were prepared from Rb. sphaeroides strain R26.1 (R26.1-RC); R26.1 RC lacking Car and a reconstituted RC (R26.1-RC+ Car) prepared by incorporating a synthetic Car (3,4-dihydrospheroidene). Although there were no detectable differences between these two RCs in their near infrared (NIR) absorption spectra at 79 and 293 K, or in their EA spectra at 79 K, significant differences were detected in their EA spectra at 293 K. Three nonlinear optical parameters of each RC were determined in order to evaluate quantitatively these differences; transition dipole-moment polarizability and hyperpolarizability (D factor), the change in polarizability upon photoexcitation (Δα), and the change in dipole-moment upon photoexcitation (Δμ*). The value of D or Δα determined for each absorption band of the two RC samples showed similar values at 77 or 293 K. However, the Δμ* values of the special pair Bchls (P) and the monomer Bchls absorption bands showed significant differences between the two RCs at 293 K. X-ray crystallography of the two RCs has revealed that a single molecule of the solubilizing detergent LDAO occupies part of the carotenoid binding site in the absence of a carotenoid. The difference in the value of Δμ* therefore represents the differential effect of the detergent LDAO and the carotenoid on P. The change of electrostatic field around P induced by the presence of Car was determined to be 1.7 × 10<sup>5</sup> [V/cm], corresponding to a 10% change in the electrostatic field around P.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Cogdell, Professor Richard and Roszak, Dr Aleksander
Authors: Yanagi, K., Shimizu, M., Hashimoto, H., Gardiner, A.T., Roszak, A.W., and Cogdell, R.J.
College/School:College of Science and Engineering > School of Chemistry
College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Journal of Physical Chemistry B
Journal Abbr.:J. Phys. Chem. B
ISSN:1520-6106
ISSN (Online):1520-5207
Published Online:24 December 2004

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