The relation between the chloride status of the photosynthetic water splitting complex and the inhibitory effectiveness of amines.

The protective role of chloride ions (Cl(-)) against inhibition of the photosynthetic water splitting complex by amines was investigated with purified photosystem II membrane particles from tobacco chloroplasts. Seemingly competitive interactions occurred between Cl(-) (except at low concentrations) and Tris, but not between Cl(-) and NH3. The rate of Cl(-) release was not increased by the amines but, instead, may have been limited by a labilization under the experimental conditions of the extrinsic 23 kDa polypeptide. An additional detachment of the 18 kDa polypeptide was seen when SO4 (2-) ions were present. Tris induced changes of the thermoluminescence patterns of flash illuminated photosystem II particles were found to be different from those caused by either Cl(-) deficiency or high pH. It is concluded that the protective functions of Cl(-) are brough about not because it is bound to the target site of the inhibitory actions of Lewis bases like amines and hydroxyl ions. Instead, this effect of Cl(-) may be due to its influence on the tertiary and quaternary structures of the water oxidizing protein complex.