CHARGE SEPARATION KINETICS IN ISOLATED PHOTOSYNTHETIC REACTION CENTERS OF CHLOROFLEXUS-AURANTIACUS (WITH QA REDUCED) AT LOW-TEMPERATURES

The picosecond fluorescence kinetics of closed (quinone acceptor Q(A) reduced) reaction centers isolated from the phototrophic bacterium Chloroflexus aurantiacus shows time constants of almost-equal-to 20 and almost-equal-to 300 ps (amplitude ratio almost-equal-to 1:1), which are nearly independent of temperature (7 to 80 K). Assuming a three-state kinetic model, we tested various assignments of the kinetics to the electron transfer processes. Only two of these assignments seem to be physically reasonable. One of these includes a fast reversible electron transfer between P* and H(M), the pheophytin(s) in the M branch of the reaction center which up to now has been considered virtually inactive in electron transfer. The other possible model involves the formation of a monomeric bacteriochlorophyll anion.