Photoelectric Responses of Oxygen-Evolving Complexes of Photosystem II

M. D. Mamedov^1*, O. E. Beshta², K. N. Gurovskaya¹, A. A. Mamedova¹, K. D. Neverov³, V. D. Samuilov², and A. Yu. Semenov¹

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

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

³Bach Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 117071 Russia

^* To whom correspondence should be addressed.

Received December 7, 1998; Revision received February 8, 1999

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The generation of a transmembrane electric potential difference induced by a series of laser flashes was studied by the direct electrometrical method in proteoliposomes containing oxygen-evolving particles of photosystem II. In addition to the fast stage of generation of the membrane potential, which is due to electron transfer from the redox active tyrosine residue Tyr-161 (Y_Z) to the primary quinone acceptor Q_A, electrogenic stages corresponding to the S₁ --> S₂ (tau = 30 µsec), S₂ --> S₃ (tau = 240 µsec), and S₃ --> S₄ --> S₀ (tau = 6.2 msec) transitions of the oxygen-evolving complex (OEC) were observed. The amplitudes of the photoelectric responses show that the contribution of the OEC to the overall electrogenicity is small. The parameters of the electrogenic reactions of the OEC as measured in photosystem II preparations containing the peripheral proteins of 23 and 17 kD were similar to those of photosystem II preparations devoid of these peptides. It is concluded that neither the 23- nor the 17-kD proteins are involved in the electrogenic reactions of the OEC.

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KEY WORDS: photosystem II, oxygen-evolving complex, proteoliposomes, S states, electrogenicity

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