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 MnCl2, the fast kinetically unresolvable phase of Δψ generation, related to electron transfer between the redox-active tyrosine YZ and the primary plastoquinone acceptor QA was followed by an additional electrogenic phase (τ∼ 20 μs, ∼5% of the phase attributed to YZoxQA-). 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 YZox. An additional electrogenicity observed upon addition of synthetic trinuclear Mn complex-1 has a τ∼ 50 μs (∼4% of the YZ oxQA) and τ∼ 160 ms (∼25%). The fast electrogenic component could be ascribed to reduction of YZ 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.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry