TRANSIENT EPR SPECTROSCOPY OF PERDEUTERATED ZN-SUBSTITUTED REACTION CENTERS OF RHODOBACTER-SPHAEROIDES R-26

Spin polarized transient EPR spectra measured in frozen solution at 9 and 24 GHz are presented for fully deuterated reaction centres of Rhod obacter sphaeroides R-26 in which the non-heme iron has been replaced by zinc. The spectra, which are assigned to the charge separated state P865+.Q(A)-. (P865 = primary chlorophyll donor, Q(A) = primary quinon e acceptor), are simulated entirely on the basis of independent experi mental data using the correlated coupled radical pair concept. From th e simulations, it is shown that it is possible to distinguish between the four possible orientations of the g tensor of P865+. obtained from high-field EPR on single crystals (Klette. Torring, Plato, Mobius, Bo nigk and Lubitz). From the excellent agreement obtained between the si mulations and the experimental results it is concluded that within the current accuracy of the X-ray structure no change in the orientation of the chromophores is induced by the charge separation.