Early reactions in green-plant photosystem I

A report is given of the recent progress in studies of the nature of the earliest electron acceptors in greenplant photosystem I and of the spectral and kinetic properties of these acceptors. These studies were carried out by optical and ESR spectroscopy methods, and also by subnanosecond detection of shortlived compounds. A sequence of the primary processes in the reaction centers of photosystem I was established. It was found that an electron passes from P700 to a primary acceptor (chlorophyll-a dimer) in less than 60 psec and then, in the next 200 psec, the anion radical of this dimer donates an electron to iron-sulfur proteins. It is concluded that the primary reactions in the centers of photosystem I are very similar to the reactions in bacterial reaction centers.