Photoelectric response generated under non-heme iron reduction on the photosystem II acceptor side

Proteoliposomes containing oxygen-evolving particles of Photosystem II and associated with a planar phospholipid membrane generate a transmembrane ele ctric potential difference (Delta Psi) induced by a laser flash. With direc t electrometrical technique, it was shown that the direction of the electri cal field ("minus" inside the proteoliposome) corresponds to acceptor side of the Photosystem II complex facing inside and donor side facing outside o f the liposomes. In addition to the fast phase (tau < 0.1 mu sec) of the De lta Psi generation due to electron transfer between Y-Z of the water-oxidiz ing complex and the primary plastoquinone Q(A), a phase with tau similar to 120 mu sec and maximum amplitude similar to 30% of the amplitude of the fa st phase was observed under the first flash in proteoliposomes containing p otassium ferricyanide, which is known as an oxidant of the non-heme iron (F e-nh) on the acceptor side of Photosystem II. This additional phase was abs ent under the second laser flash but was completely restored after 5 min da rk adaptation. The phase of the photoelectric response with tau similar to 120 mu sec is probably due to electron transfer from Q(A) to Fe-nh(III) and likely includes a component related to H+ transfer.