Electrogenicity accompanies photoreduction of the iron-sulfur clusters F A and F B in photosystem I

Abstract

Photovoltage responses accompanying electron transfer on the acceptor side of photosystem I (PS I) were investigated in proteoliposomes containing PS I complexes from the cyanobacterium Synechococcus sp. PCC 6301 using a direct electrometrical technique. The relative contributions of the F X→F B and the F X→F A electron transfer reactions to the overall electrogenicity were elucidated by comparing the sodium dithionite-induced decrease in the magnitude of the total photoelectric responses in control and in F B-less (HgCl 2-treated) PS I complexes. The results obtained suggest that the electrogenesis on the acceptor side of PS I is related to electron transfers between both F X and F A and F A and F B. Based on the electrogenic nature of the latter reaction in PS I complexes, we conclude that F A rather than F B is the acceptor proximal to F X.