The kinetics of bacteriochlorophyll fluorescence in intact cells of the purple nonsulfur bacterium Rhodobacter sphaeroides were measured under continuous and pulsed actinic laser diode (808 nm wavelength and maximum 2 W light power) illumination on the micro- and millisecond timescale. The fluorescence induction curve was interpreted in terms of a combination of photochemical and triplet fluorescence quenchers and was demonstrated to be a reflection of redox changes and electron carrier dynamics. By adjustment of the conditions of single and multiple turnovers of the reaction center, we obtained 11 ms-1 and 120 μs-1 for the rate constants of cytochrome c23+ detachment and cyclic electron flow, respectively. The effects of cytochrome c2 deletion and chemical treatments of the bacteria and the advantages of the fluorescence induction study on the operation of the electron transport chain in vivo were discussed., G. Sipka, M. Kis, J. L. Smart, P. Maróti., and Obsahuje bibliografické odkazy
Electrochromic changes of the Qy absorption bands of chromophores (dimeric and monomeric bacteriochlorophylls and bacteriopheophytins) were measured in reaction centres from purple photosynthetic bacteria Rhodobacter sphaeroides. The observed electrochromic effects could be decomposed to changes dne to negative charge on the acceptor quinone complex and positive charge on the dimer. The coiďumed additivity (superposition) of the electrochromic effects indicated that the chromophores had fixed geometry in redox transitions. The Qy absorption band of the bacteriopheophytin proved to be a very sensitive indicator of the relaxational processes of electric charges (protons and/or cations) in the vicinity of the quinones: (7) the bandwidth was affected by pH around 10 which was close to the pK of protonation of the reduced primary quinone, (2) absorption changes at 748 nm were observed after flash excitation with time constant characteristic to that of light- induced proton binding in reaction centres.