Bicarbonate and Function of Photosytem II

The scope of this work is an identifying functional place of bicarbonate (HCO3 − ) in photosystem II. Both exogenous bicarbonate and formate (HCO2 − ) stimulate the increase of variable fluorescence of chlorophyll. However, the increase of fluorescence is not enhanced by combined action of HCO3 − and HCO2 − . It was found that formate inhibits the formation of the S2 state multiline EPR signal (g = 2.00) concomitant with stimulation of the QA •–Fe2+ signal at g = 1.82. Similarly to the multiline signal intensity, formate also inhibite the oxygen evolution function of PSII. The inhibitory effects of formate give the impression to the retarded electron transfer from water oxidation center to the tyrosine YZ • . The results suggests that the acceptor side of photosystem II is a HCO3 − -functional site, while the formate effects ascribed both the acceptor and donor side of photosystem II. Instead of earlier studies, clayming that BC can accelerate electron transfer in both acceptor and donor side of PSII, in this study the function of bicarbonate is suggested as delaying the electron flow in its acceptor side.