ELECTRON TRANSFER THROUGH PHOTOSYSTEM II ACCEPTORS.::INTERACTION WITH ANIONS

We present an overview of anionic interactions with the oxidationreduction reactions of photosystem II (PSII) acceptors. In section I, a framework is lald for the electron ~cceptor side of PSII: the overview begins with a current scheme of the electron transport pathway and of the localization of components in the thylakoid membrane, which is followed by a brief description of the electron acceptor Q or QA and the various heterogeneities associated with it. In section 2, we review briefly the nature of the active species of the bicarbonate (HC03) effect, the location of the site of action of HCO], and its Pelatlonship to interactions with other anions. In section 3,-we review data on the anion effects on the reoxldation of QA and on the various reactions involved in the twoelectron gate mechanism of PSII,~and prOvldela:hypothesis as to the action of HCO 3 on the protonation reactions. New data ~btalned by one of us (G) in collaboration with J.J.S. van Rensen, J.F.H Sne! and W. Tonk for HCO3deplete