Electron transfer through photosystem II acceptors: Interaction with anions

Abstract

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 HCO3-depleted thylakolds, demonstrating the abolition iof the binary oscill~-tlons contained within the periodicity of 4 observed for proton release, are also reviewed.In section 4, we comment on t~e measured binding constant of HCO3 at the anion binding site. And, in section 5, we review our current concept of the mechanism of the HCO3 effect on the electron accepter side of PSII, and_comment on the possible physiological roles for HCO 3.Measurements of HCOg reverslble anionle inhlbltlon in intact cells of ~ green alga Soenedesmus-are also reviewed.

Regulation of photosynthetic pigments in micro‐algae by multiple environmental factors: a dynamic balance hypothesis

“…It was modelled as a function of the likelihood of the receipt by a PSU of one or more photons within the time frame of the rate-limiting step in the linear electron transport chain leading to reduction of COg. This time domain is in the 1-3 ms range, whether one is considering limitations due to water oxidation, plastoquinone redox turnover, or Rubisco kinetics (Govindjee & Eaton-Rye, 1986;Sukenik, Bennett & Falkowski, 1987;Falkowski, 1992).…”

Bicarbonate-controlled reduction of oxygen by the Q A semiquinone in Photosystem II in membranes

“…S7 B ). Formate, at 100 mM, a concentration known to be competitive with bicarbonate ( 25 , 26 ), behaved like bicarbonate: it prevented from reducing O 2 ( SI Appendix , Fig. S7 B ).…”