PRIMARY CHARGE SEPARATION IN PHOTOSYSTEM-I - A 2-STEP ELECTROGENIC CHARGE SEPARATION CONNECTED WITH P700(-) AND P700(+)A(1)(-) FORMATION()A(0)()

A PS I membrane preparation from a PS II deficient mutant of Synechocy stis sp. PCC 6803 (psb DI/DII/C-) was investigated by picosecond photo voltage and fluorescence measurements. The photovoltage kinetics show two distinct phases. At low excitation energies the fast phase correla tes with the fluorescence decay time constant of 22 +/- 4 ps. This pha se is ascribed to the trapping of excitons as described by the reactio n (Ant(i)P700)() A(0) --> Ant(i)P700(+) A(0)(-). In addition to this phase, the photovoltage displays a second rising phase of smaller ampl itude with a time constant of 50 +/- 15 ps. We assign the latter phase to further electron tranfer from A(0) to the secondary acceptor, A(1) . Assuming the protein as a homogeneous dielectric, our results sugges t that the transmembrane distance A(0)-A(1) spans only a small part (2 0 +/- 8%) of the distance P700-A(1).