Light-Induced Charge Separation between Plastocyanin and the Iron–Sulfur Clusters FAand FBin the Complex of Plastocyanin and Photosystem I

The light-induced electron transfer in a crosslinked complex between plastocyanin and photosystem I from spinach was studied by EPR at low temperature. Electron donation from reduced plastocyanin to P700+was observed under illumination above a temperature of about 160 K, resulting in a second charge separation and an electron transfer from rereduced P700 to the terminal electron acceptors FA/FB. The charge-separated state PcoxP700+[FA/FB]2−was found to be stable at 15 K. Implications of these results for the kinetic constants of the donation reaction and the backtransfer of electrons from reduced acceptors as well as for the structural models of the terminal acceptors are discussed.