Electrogenic reactions on the donor side of Mn-depleted photosystem II core particles in the presence of MnCl2 and synthetic trinuclear Mn-complexes

An electrometric technique was used to investigate the generation of a photovoltage (Δψ) by Mn-depleted spinach photosystem II (PS II) core particles incorporated into liposomes. In the presence of MnCl 2 , the fast kinetically unresolvable phase of Δψ generation, related to electron transfer between the redox-active tyrosine Y Z and the primary plastoquinone acceptor Q A was followed by an additional electrogenic phase ( τ ∼ 20 μs, ∼5% of the phase attributed to Y Z ox Q A − ). The latter phase was ascribed to the transfer of an electron from the Mn, bound to the Mn-binding site of the PS II reaction center to the Y Z ox . An additional electrogenicity observed upon addition of synthetic trinuclear Mn complex-1 has a τ ∼ 50 μs (∼4% of the Y Z ox Q A ) and τ ∼ 160 ms (∼25%). The fast electrogenic component could be ascribed to reduction of Y Z ox by Mn , delivered to the Mn-binding site in Mn-depleted samples after the release of the tripod ligands from the complex-1 while the slow electrogenic phase to the electron transfer from the Mn-containing complex-1 attached to the protein- water boundary to the oxidized Mn at the protein-embedded Mn -binding site.