Dynamics of excitation in the photosystem I of cyanobacteria: transfer in the antenna, capture by the reaction site, and dissipation

The structure of a complex of photosystem I (PSI) of cyanobacteria and the mechanisms of the functioning of the antenna and PSI reaction site were described. The complex of PSI in thylakoids of cyanobacteia is organized as a trimer whose antenna is enriched in long-wave chlorophylls. The energy absorbed by these chlorophyls migrates to P700, inducing its oxidation. Long-wave chlorophyls are also involved in the dissipation of excessive energy; both the cation radical of P700 and the triplet of P700 effectively quench the fluorescence of long-wave chlorophyll of PSI. The energy exchange between the antennas of monomers in the trimer of PSI stimulates the dissipation of electron excitation energy, protecting the complex against photodestruction. The kinetics of energy migration in the antenna and charge separation in the reaction site of PSI trimers was studied using subpicosecond spectroscopy. Long-wave chlorophylls of PSI do not substantially affect the energy migration in the heterogeneous antenna of PSI but slow down the capture of energy of P700. The separation of changes in the reaction site of PSI is the most rapid among the known reaction sites.