PRIMARY PROCESSES AND STRUCTURE OF THE PHOTOSYSTEM-II REACTION-CENTER .2. LOW-TEMPERATURE PICOSECOND FLUORESCENCE KINETICS OF A D1-D2-CYT-B-559 REACTION-CENTER COMPLEX ISOLATED BY SHORT TRITON EXPOSURE

The fluorescence kinetics of a D1-D2-cyt-b-559 reaction center complex isolated by short Triton-exposure has been measured with picosecond resolution as a function of temperature below 150 K. The data were analyzed by combined global analysis of data measured with different time resolutions and are presented as decay-associated fluorescence spectra (DAS). Emphasis is given to the resolution and assignment of the fast components below 100 ps. Six lifetime components were generally necessary for a good fit of the data over a long time-range. The shortest lifetime of 13-24 ps (depending on temperature) is attributed to an energy transfer from (accessory) Chlorophyll to P680, presumably via pheophytin. A component in the range of 40-70 ps is attributed to energy transfer from pheophytin to P680. These components can only be properly resolved and assigned from measurements at temperatures below about 40 K. An ultrashort component of 1-6 ps, which had been resolved in our previous measurements (Biochim. Biophys. Acta (1991) 1060, 237-244) was not resolved in the particles studied here. We propose that the absence of the ultrashort component in this study is attributable to the larger chlorophyll content of the present short-term Triton-exposed D1-D2-cyt-b-559 preparation as compared to the previous long-term Triton-exposed RC particles. In the particles studied here the effective charge separation kinetics in the short time-range is rate-limited by relatively slow energy transfer components (lifetimes from 13 to 24 ps) upon preferential excitation of the accessory chlorophylls. In the long time-range a multicomponent charge recombination kinetics giving rise to four fluorescence lifetimes in the range of 1.56-49.7 ns are resolved. All these components show basically identical DAS with maxima near 682 nm.