EFFECTS OF SELECTIVE DESTRUCTION OF IRON-SULFUR CENTER-B ON ELECTRON-TRANSFER AND CHARGE RECOMBINATION IN PHOTOSYSTEM-I

Incubation of spinach thylakoids with HgCl2 selectively destroys Fe-S center B (F(B)). The function of electron acceptors in F(B)-less PS I particles was studied by following the decay kinetics of P700+ at room temperature after multiple flash excitation in the absence of a terminal electron acceptor. In untreated particles, the decay kinetics of the signal after the first and the second flashes were very similar (t1/2 approximately 2.5 ms), and were principally determined by the concentration of the artificial electron donor added. The decay after the third flash was fast (t1/2 approximately 0.25 ms). In F(B)-less particles, although the decay after the first flash was slow, fast decay was observed already after the second flash. We conclude that in F(B)-less particles, electron transfer can proceed normally at room temperature from F(X) to F(A) and that the charge recombination between P700+ and F(X)-/A1- predominated after the second excitation. The rate of this recombination process is not significantly affected by the destruction of F(B). Even in the presence of 60% glycerol, F(B)-less particles can transfer electrons to F(A) at room temperature as efficiently as untreated particles.