On the electron stabilization within the quinone acceptor part of Rhodobacter sphaeroides photosynthetic reaction centers

: The time evolution of the photoinduced differential absorption spectrum of isolated Rhodobacter sphaeroides photosynthetic reaction centers was investigated. The measurements were carried out in the spectral region of 400-500 nm on the time scale of up to 200 microseconds. The spectral changes observed can be interpreted in terms of the effects of proton shift along hydrogen bonds between the primary quinone acceptor and the protein. A theoretical analysis of the spectrum time evolution was performed, which is based on the consideration of the kinetics of proton tunneling along the hydrogen bond. It was shown that the stabilization of the primary quinone electronic state occurs within the first several tens of microseconds after quinone reduction. It slows down upon the deuteration of reaction centers as well as after adding 90% of glycerol; on the other hand, it accelerates as temperature rises up to 40 degrees C.