TIME-RESOLVED TRYPTOPHAN FLUORESCENCE IN PHOTOSYNTHETIC REACTION CENTERS FROM RHODOBACTER-SPHAEROIDES

Tryptophan fluorescence of reaction centers isolated from Rhodobacter sphaeroides, both stationary and time-resolved, was studied. Fluoresce nce kinetics were found to fit best a sum of four discrete exponential components. Half of the initial amplitude was due to a component with a lifetime of congruent-to 60 ps, belonging to Trp residues, capable of efficient transfer of excitation energy to bacteriochlorophyll mole cules of the reaction center. The three other components seem to be em itted by Trp ground-state conformers, unable to participate in such a transfer. Under the influence of intense actinic light, photooxidizing the reaction centers, the yield of stationary fluorescence diminished by congruent-to 1.5 times, while the number of the kinetic components and their life times remained practically unchanged. Possible implica tions of the observed effects for the primary photosynthesis events ar e considered.