FORMATION OF CHARGE SEPARATED STATE P(-) AND TRIPLET-STATE P-3 AT LOW-TEMPERATURE IN RHODOBACTER-SPHAEROIDES (R-26) REACTION CENTERS IN WHICH BACTERIOPHEOPHYTIN A IS REPLACED BY PLANT PHEOPHYTIN A()Q(A)()

Low temperature optical and photochemical properties of Rhodobacter sp haeroides (R-26) reaction centers, in which bacteriopheophytin a has b een replaced by plant pheophytin <alpha a, are reported. Modified reac tion centers preserve the ability for photoinduced electron transfer f rom the primary electron donor P to the primary quinone acceptor Q(A) at 80K. The triplet state ESR signal of modified reaction centers with prereduced Q(A) at 10K shows an electron spin polarization pattern an d ZFS parameters analogous to those for the triplet state P-3 in non-t reated reaction centers. It was found that at low temperature both P()Q(A)(-), and P-3 states are formed via a precursor radical pair P+I- in which I is the introduced plant pheophytin molecule. This shows tha t acceptor systems of bacterial and plant (photosystem II) reaction ce nters are mutually replacable in structural and functional aspects.