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 (Delta psi) by Mn-depleted spinach photosystem II (PS II) core particles incorporated into liposomes. In the presence of MnCl2, the fast kinetically unresolvable phase of Delta psi 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 (tau similar to 20 mu s, similar to 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 tau similar to 50 ms (similar to 4% of the Y(Z)(ox)Q(A)) and tau similar to 160 ms (similar to 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.