Charge separation kinetics in isolated photosynthetic reaction centers of Chloroflexus aurantiacus (with Q A reduced) at low temperatures

Abstract

The picosecond fluorescence kinetics of closed (quinone acceptor Q A reduced) reaction centers isolated from the phototrophic bacterium Chloroflexus aurantiacus shows time constants of ≈ 20 and ≈ 300 ps (amplitude ratio ≈ 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.