PRIMARY CHARGE SEPARATION PROCESSES IN REACTION CENTERS OF AN ANTENNA-FREE MUTANT OF RHODOBACTER-CAPSULATUS

The primary charge separation processes of membrane-bound reaction cen ters from an antenna-free mutant of the purple bacterium Rhodobacter c apsulatus have been investigated by picosecond time-resolved fluoresce nce and femtosecond stimulated emission measurements. Target analysis has been applied to decompose the time-resolved fluorescence emission spectrum into its components for open and closed (quinone-reduced) rea ction centers. The reaction center environment, i.e. membrane vs. dete rgent, exerts a remarkable influence on the primary charge separation kinetics. For fully open reaction centers the main component of the pr imary electron transfer process from the excited special pair to bacte riopheophytin measured both in fluorescence and in femtosecond stimula ted emission - takes 5-6 ps, which is a factor of nearly two longer th an in the corresponding detergent-isolated reaction centers (2.7 ps). For quinone-reduced RCs a very long charge separation time of approx. 10 ps is observed, concomitant with a more than five-fold increase in fluorescence yield. All of these parameters differ substantially from those of detergent-isolated RCs. Possible origins for the observed kin etics are discussed.