Picosecond fluorescence kinetics of the D1-D2-cyt-b-559 photosystem II reaction center complex. Energy transfer and primary charge separation processes

The fluorescence kinetics of the D 1 -D 2 -cyt- b -559 Photosystem II reaction-center complex have been characterized in the picosecond and nanosecond time ranges. Measurements have been performed in the presence of β-lauryl maltoside under anaerobic conditions, both at 277 K and 77 K. Global analysis of decays recorded at different wavelengths and with different time resolutions yielded the decay-associated emission spectra of six exponential lifetime components, in the range of 1–6 ps up to 35 ns. We report here an ultrafast (τ≈1–6ps) fluorescence lifetime component with dominant amplitude (≥90%), which is thought to reflect the primary charge separation process. Furthermore, we have resolved a component with a 30–40 ps lifetime, its DAS indicating energy transfer. The lifetime of the primary radical pair P 680 + I ∼ , reflected by its recombination fluorescence, was found to be temperature-dependent. At 277 K this lifetime was 30 ns with a relative yield of 0.87, whereas at 77 K the radical-pair lifetime is increased to 35 ns with a relative yield of only 0.24 (both yields are corrected for the emission from uncoupled chlorophylls).