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 sphaer oides strain RCO1 has been extended to an investigation of the kinetic s and spectroscopy of primary charge separation. Global analysis of ti me-resolved difference spectra demonstrated that the rate of charge se paration in membrane-bound reaction centers is slightly slower than in detergent-solubilized reaction centers from the same strain. A kineti c analysis of the decay of the primary donor excited state at single w avelengths was carried out using a high repetition rate laser system, with the reaction centers being maintained in the open state using a c ombination of phenazine methosulfate and horse heart cytochrome c. The kinetics of primary charge separation in both membrane-bound and solu bilized reaction centers were found to be non-monoexponential, with tw o exponential decay components required far a satisfactory description of the decay of the primary donor excited state. The overall rate of charge separation in membrane-bound reaction centers was slowed if the primary acceptor quinone was reduced using sodium ascorbate. This slo wing was caused, in part, by an increase in the relative amplitude of the slower of the two exponential components. The acceleration in the rate of charge separation observed on removal of the reaction center f rom the membrane did not appear to be caused by a significant change i n the electrochemical properties of the primary donor. The influence o f the environment of the reaction center on primary charge separation is discussed together with the origins of the non-monoexponential deca y of the primary donor excited state.