PRIMARY DONOR STATE MODE STRUCTURE AND ENERGY-TRANSFER IN BACTERIAL REACTION CENTERS

Temperature-dependent photochemical hole burning data for P870 of Rhodobacter sphaeroides reaction centers (RC) are reported which lead to a determination for the mean frequency of the protein phonons which couple to the optical transition. Utilization of this frequency, ωm ∼ 25-30 cm-1, together with improved functions for the single site (RC) absorption line shape and inhomogeneous broadening is shown to lead to significant improvement in the theoretical fits to the hole and absorption spectra (including those of P960 of Rhodopseudomonas viridis). Time-dependent P870 hole spectra are reported which provide additional evidence that the previously observed zero-phonon hole is an intrinsic feature of P870 for active RC. Transient spectra obtained by laser excitation into the accessory Qy-absorption bands of the RC are presented which show an absence of both line narrowing and a dependence on the location of the excitation frequency. These results, which are consistent with ultrafast energy-transfer processes from the accessory states, are discussed in terms of earlier time domain data. © 1990 American Chemical Society.