Time-resolved and steady-state spectroscopic analysis of membrane-bound reaction centers from Rhodobacter sphaeroides: comparisons with detergent-solubilized complexes.

The spectroscopic analysis of the antenna-deficient Rhodobacter sphaeroides strain RCO1 has been extended to an investigation of the kinetics and spectroscopy of primary charge separation. Global analysis of time-resolved difference spectra demonstrated that the rate of charge separation in membrane-bound reaction centers is slightly slower than in detergent-solubilized reaction centers from the same strain. A kinetic analysis of the decay of the primary donor excited state at single wavelengths was carried out using a high repetition rate laser system, with the reaction centers being maintained in the open state using a combination of phenazine methosulfate and horse heart cytochrome c.

Site-specific mutagenesis of the reaction centre from Rhodobacter sphaeroides studied by Fourier transform Raman spectroscopy: mutations at tyrosine M210 do not affect the electronic structure of the primary donor.

The effects of mutation of residue tyrosine M210 on the primary donor bacteriochlorophylls have been investigated by near infrared FT-Raman spectroscopy in reaction centres purified from an antenna-deficient strain of Rhodobacter sphaeroides. We find that mutation at the M210 position does not significantly perturb the distribution of the unpaired electron over the pair of bacteriochlorophyll molecules which constitute the primary donor radical cation. We conclude, therefore, that the effects of mutation of tyrosine M210 on the rate and asymmetry of primary electron transfer in reaction centres cannot be ascribed to a change in the electronic structure of the primary donor.