Spectroscopic resolution of the picosecond reduction kinetics of the secondary electron acceptor A₁ in photosystem I

Forward electron transfer in photosystem I from Synechocystis sp. PCC 6803 has been studied in the picosecond time range with transient absorption spectroscopy in the blue and near-UV spectral regions. From the direct measurement, at 380-390 nm, of the reduction kinetics of the phylloquinone secondary acceptor A₁ and from the absence of spectral evolution between 100 ps and 2 ns, we conclude that electron transfer, from the chlorophyll a primary acceptor A₀, to A₁ occurs directly and completely with a time constant of about 30 ps. Copyright (C) 1999 Federation of European Biochemical Societies.