The photosystem I trimer of cyanobacteria: molecular organization, excitation dynamics and physiological significance

The photosystem I complex organized in cyanobacterial membranes preferentia lly in trimeric form participates in electron transport and is also involve d in dissipation of excess energy thus protecting the complex against photo damage, A small number of longwave chlorophylls in the core antenna of phot osystem I are not located in the close vicinity of P700, but at the periphe ry, and increase the absorption cross-section substantially. The picosecond fluorescence kinetics of trimers resolved the fastest energy transfer comp onents reflecting the equilibration processes in the core antenna at differ ent redox states of P700, Excitation kinetics in the photosystem I bulk ant enna is nearly trap-limited, whereas excitation trapping from longwave chlo rophyll pools is diffusion-limited and occurs via the hulk antenna. Charge separation in the photosystem I reaction center is the fastest of all known reaction centers. (C) 1999 Federation of European Biochemical Societies.