Abstract
The reaction center (RC) of heliobacteria seems to have evolved from an ancestor common with photosystem (PS) I RC of cyanobacteria and plants. However, the reaction of quinone that is obvious in PS I heterodimeric RC has never been evidenced in heliobacterial RC. The RC as well as that of green sulfur bacteria, which is also type-1, are considered to form the symmetrical homodimeric structure. We previously carried out the nanosecond absorption spectroscopy of the primary electron acceptor A0 at 77K in two different RC preparations from Heliobacterium modesticaldum, and showed that re-oxidation of the photo-oxidized P798+ occurs with a t1/2 = 2 ms, presumably ascribable to the charge recombination between the reduced Fe-S centers and P798+. No indication of the quinone function was detected. We here report the FA- and FB-like ESR signals in the membrane preparations and discuss their detailed features in terms of the electron transfer mechanism.
