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 D1-D2-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 beta-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 (tau almost-equal-to 1-6 ps) fluorescence lifetime component with dominant amplitude (greater-than-or-equal-to 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 P680+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).