An electrometrical technique was used to investigate flash-induced electron transfer reactions between Mn-depleted spinach photosystem II core particles incorporated into liposomes and redox mediators. Besides the fast increase in the transmembrane electric potential difference associated with electron transfer between the redox active tyrosine (YZ) and the primary quinone acceptor QA, an additional electrogenic phase was observed in the presence of N,N,N′N′-tetramethyl-p-phenylenediamine and 2,6-dichlorophenol-indophenol. The latter phase is attributed to vectorial electron transfer from the redox dye(s) to the protein-embedded YZ. The data obtained suggest an electrically isolated location of the YZ from the external water phase.
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