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

Localisation of the accumulated chlorophyll cation in the Photosystem II reaction centre. Frantisek Vacha^*,1, Jakub Psencik^{2, 3}, Milan Durchan^{1, 3}, Mirek Dusin⁴, ¹ Institute of Plant Molecular Biology ASCR, Ceske Budejovice, Czech Republic² Faculty of Mathematics and Physics, UK, Praha, Czech Republic³ Institute of Physical Biology, Nove Hrady, Czech Republic⁴ Institute of Rychle Sipy, Praha, Czech Republic

ABSTRACT- Structure and function of the reaction centre of photosystem II was studied by means of combination of experimental spectroscopy and theoretical approach. Absorption and circular dichroism spectra of isolated photosystem II reaction centres were compared with spectra calculated on the basis of point-dipole approximation, using the pigment orientation of several latest published structures of photosystem II reaction centre. Applicability of the method was tested on spectra calculated on the more precise structure of the reaction centres of purple bacteria. This combined approach was used to localise the chlorophyll cation by a light induced charge accumulation in photosystem II reaction centre. Chlorophyll cation was accumulated during a light treatment of Photosystem II reaction centre in the presence of artificial electron acceptor, silicomolybdate, in a time scale of seconds. The accumulation of chlorophyll cation was detected in the absorption spectra of photosystem II reaction centre as a decrease of absorption at 680 nm. Complex changes in CD spectra were also observed. Simulations of light induced absorption and CD difference spectra were calculated. In these calculations, one of the six chlorophylls was always step by step omitted from each calculation. The experimental light induced absorbance and CD difference spectra were compared with their calculated counterparts where different individual chlorophylls were missing. As a conclusion we suggest that during the light treatment of photosystem II reaction centre in the presence of electron acceptor the positive charge is accumulated on the accessory chlorophyll of the active branch on the D1 protein.

KEY WORDS: reaction centre, circular dichroism, spectroscopy, charge separation