PARENT SESSION
Posters P6A Type II reaction centres: Excited state dynamics and donor side. Abstracts (313-346)

Theory of optical spectra of Photosystem II reaction centers: From structure to function. Thomas Renger^*,1, Grzegorz Raszewski¹, Wolfram Saenger¹, ¹ Freie Universität Berlin, Institut für Chemie, Berlin, Germany

ABSTRACT- The recent progress in structural analysis of Photosystem II of T. elongatus [1] provides the orientation of optical transition dipoles of the reaction center pigments and the distances between them. Based on this knowledge a detailed calculation of optical properties (absorption, linear and circular dichroism, fluorescence, absorption difference with triplet and with exchanged pheophytin) of D1-D2 reaction center complexes is presented. For the description of the spectra a density matrix theory is used that includes, both, an exciton relaxation induced life time broadening and vibrational sidebands of optical transitions [2]. The calculations of the spectra and comparison with experimental data [3-5] are used to extract the local optical transition energies of the reaction center pigments, the so-called site energies. The site energies are then verified by calculations and comparison with independent experimental data of D1-D2 complexes [4] and difference spectra (triplet minus singlet, oxidized minus singlet) of Photosystem II core complexes [6]. The accessory chlorophyll of the D1-branch is found to exhibit properties that are unique among the reaction center pigments: (i) it has the lowest site energy, (ii) the triplet at low temperatures is located at this chlorophyll, (iii) its site energy is temperature dependent, and (iv) its site energy in D1-D2 complexes differs from that in core complexes. The site energies of the pigments are used to study exciton relaxation and primary electron transfer in the reaction center. Evidence is provided for the accessory chlorophyll of the D1-branch as being the primary electron donor in Photosystem II. References : [1] J. Biesiadka, B. Loll, J. Kern, K. D. Irrgang, W. Saenger, A. Zouni (in preparation). [2] Th. Renger and R. A. Marcus, J. Chem. Phys. 116 (2002) 9997. [3] M. Germano, A. Shkuropatov, H. Permentier, R. de Wijn, A. J. Hoff, V. A. Shuvalov, H. J. van Gorkom, Biochemistry 40 (2001) 11472. [4] M. Germano, A. Shkuropatov, H. Permentier, R. A. Khatypov, V. A. Shuvalov, A. J. Hoff, H. J. van Gorkom, Photosyn. Res. 64 (2000) 189. [5] L. Konermann, A. R. Holzwarth, Biochemistry 35 (1996) 829. [6] B. Hillmann, K. Brettel, F. van Mieghem, A. Kamlowski, W. A. Rutherford, E. Schlodder, Biochemistry 34 (1995) 4814.

KEY WORDS: exciton transfer, optical spectra, photosystem II, electron transfer