Photoelectric Response Generated under Non-Heme Iron Reduction on the Photosystem II Acceptor Side

M. D. Mamedov^1*, O. E. Beshta², N. I. Shutilova³, A. Yu. Semenov¹, and V. D. Samuilov²

¹Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-3181; E-mail: mahir@electro.genebee.msu.su

²School of Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-3807

³Institute of the Basic Problems of Biology, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia

^* To whom correspondence should be addressed.

Received September 24, 1999; Revision received October 18, 1999

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Proteoliposomes containing oxygen-evolving particles of Photosystem II and associated with a planar phospholipid membrane generate a transmembrane electric potential difference (DeltaPsi) induced by a laser flash. With direct electrometrical technique, it was shown that the direction of the electrical field (“minus” inside the proteoliposome) corresponds to acceptor side of the Photosystem II complex facing inside and donor side facing outside of the liposomes. In addition to the fast phase (tau < 0.1 µsec) of the DeltaPsi generation due to electron transfer between Y_Z of the water-oxidizing complex and the primary plastoquinone Q_A, a phase with tau ~ 120 µsec and maximum amplitude ~30% of the amplitude of the fast phase was observed under the first flash in proteoliposomes containing potassium ferricyanide, which is known as an oxidant of the non-heme iron (Fe_nh) on the acceptor side of Photosystem II. This additional phase was absent under the second laser flash but was completely restored after 5 min dark adaptation. The phase of the photoelectric response with tau ~ 120 µsec is probably due to electron transfer from Q_A to Fe_nh(III) and likely includes a component related to H⁺ transfer.

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KEY WORDS: Photosystem II, non-heme iron, proteoliposomes, electrogenesis

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