3-dimensional configuration of the electron transfer chain in photosynthesis studied by pulsed EPR

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a) ELDOR of 3-spin systems to investigate the configuration of electron transfer componentsSo far we have obtained the distances between Tyrosines Z(Y_Z) and D(Y_D), and Q_A and Y_D in spinach photosystem II. To investigate the unknown distance between Q_A and Y_Z, pulsed ELDOR was applied to a 3-spin system Y_D^・-Y_Z^・-Q_A^-. As all the 3-spin systems could not be always trapped, simulation was carried out for assumed ratios of the three spin system and other pair of two spin systems to fit the observed time profile. The best fit distance for Q_A-Y_Z was 34 A. To confirm, ELDOR of Q_A^<->-Y_Z^・ was observed in a Y_D-less mutant of Chlamydomonas reinhardtii. A graphical method was proposed to get positions of all the electron transfer components.b) Determination of the functional site.When electron transfer is inhibited, a chlorophyll near by the reaction center gives an electron to P680^+ instead of the second donor Y_Z and the oxidized chlorophyll was named Chl_Z^・. However, which chlorophyll in D1 or D2 proteins act functional, has not yet determined. ELDOR for Y_D-Chl_Z provided that the distance between these radicals was 29.5 A. ELDOR of Y_D^・-Chl_Z^・-Q_A^- system and Y_Z^・-Chl_Z^・. In the Y_D-less mutant revealed the accessory chlorophyll on the D2 protein is the functional site.c) Change in the spin configuration on four manganese site on oxidation,The distances of the Mn-cluster in the S_0 and S_2 states, respectively, from Y_D have been shown to be 7 A different. Assuming the simple dipolar interaction the spin center of the Mn-cluster approached from S_0 to S_2 state to the Y_D site. This value seems to be too large based on the recent X-ray analysis. Taking account of spin projections on each Mn-ion, detailed simulations are being undertaken in cooperation with Bittl in Free University Berlin.