A dynamic interaction between the bicarbonate ligand and photosystem II reaction center complexes in chloroplasts.

The binding of HCO-3 to Photosystem II reaction center complexes in broken chloroplasts requires the presence of the oxidized form of the negative charge accumulator 'B'. HCO-3 which is already bound to the reaction center II complex can escape if chloroplasts are illuminated with saturating light in the presence of a Hill oxidant and high concentrations of sodium chloride and sodium formate. These observations are explained in terms of a cyclic dark binding of HCO-3 to the reaction center II complex and a subsequent release in the light.