Energy Transfer in Rhodobacter sphaeroides Reaction Centers with the Initial Electron Donor Oxidized or Missing

Energy transfer between chromophores in the reaction center of Rhodobacter sphaeroides R-26 with and without the initial donor oxidized and in reaction centers from the strain VR(L157) that has the mutation Val to Arg at L157 has been investigated using femtosecond transient absorption spectroscopy. Pigment extractions and an analysis of the ground-state absorbance spectrum indicate that VR(L157) reaction centers have a substantial reduction in the amount of bacteriochlorophyll present per reaction center, due to the loss of one or both of the bacteriochlorophylls in the initial electron donor (P). The QY transition bands of the bacteriochlorophyll monomers (B) and the bacteriopheophytins (H) in reaction centers from the three reaction center samples (R-26 with and without P oxidized and VR(L157)) were selectively excited using 150 fs duration, 5 nm bandwidth pulses, and transient absorbance spectra were recorded. Quenching of the lowest excited state of the bacteriochlorophyll monomer (B*) occurs in hund...