Rates of Primary Electron Transfer Reactions in the Photosystem I Reaction Center Reconstituted with Different Quinones as the Secondary Acceptor

Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi]]) are measured by picosecond absorption spectroscopy in spinach photosystem I (PS I) particles. In the particles, 85-90% of antenna chlorophylls are extracted and the intrinsic phylloquinone (Q[sub [phi]]) is removed and replaced by different quinones. (1) The excited single state of P700, monitored by the absorbance change at 695 nm, appeared with a time constant shorter than 1 ps after excitation with a 605 nm, 1 ps pulse at an intensity of 0.8 or 1.5 photons/reaction center. Indication for the absorbance change of the chlorophylls, which may function as the intermediate electron acceptor between P700 and A[sub 0] or between A[sub 0] and Q[sub [phi]], was not obtained. 45 refs., 5 figs., 1 tab.