Inhibition of oxygen evolution in Photosystem II by Cu(II) ions is associated with oxidation of cytochrome b559.

We have found that elevated copper concentrations, apart from the inhibition of oxygen evolution, changed the initial states distribution of the oxygen-evolving complex. Already at low concentrations, copper ions oxidized the low-potential form of cytochrome b (559) and also its high-potential form at higher concentrations at which fluorescence quenching was observed. We suggest that the primary target sites in Photosystem II for copper is tyrosine(z), both cytochrome b (559) forms and chlorophyll(z), and that these sites are the source of the copper-induced fluorescence quenching and oxygen evolution inhibition in Photosystem II.