PULSED ENDOR OF THE PHOTOEXCITED TRIPLET-STATES OF BACTERIOCHLOROPHYLL A AND OF THE PRIMARY DONOR P-865 IN REACTION CENTERS OF RHODOBACTER-SPHAEROIDES R-26

The photoexcited tripler states of bacteriochlorophyll a, (3)BChl a, a nd of the primary donor in reaction centers of Rhodobacter sphaeroides R-26, P-3(865), are investigated by pulsed EPR and ENDOR spectroscopy . In P-3(865) a splitting of ENDOR lines and reduction of correspondin g positive and negative hyperfine couplings as compared with the monom eric (3)BChl a is observed. This indicates an asymmetric distribution of the triplet excitation over the two BChl a moieties, P-L and P-M fo rming P-3(865). Based on the signs of the hyperfine couplings and on a comparison with the cation and anion radical of BChl a an assignment to nuclei in the different dimer halves is proposed. This yields an es timate for the extent of delocalization of the triplet excitation over P-L and P-M and for the charge transfer contribution of P-3(865).