Atrazine Inhibition of Photosystem II is Modulated By Specific Inorganic Cofactors Involved in Oxygen Evolution

Abstract

The photosynthetic oxygen evolving complex is located toward the inner surface of the thylakoid and includes three extrinsic polypeptides of approximate molecular weights 16, 23 and 33 kDa. Three inorganic cofactors namely Cl−, Ca2+ and Mn2+ are also established to be associated with the oxygen evolving complex (for a review see ref. 1). However, the relationships between the extrinsic polypeptides and the above inorganic components are not clearly understood. it is assumed that 33 kDa polypeptide is probably essential for maintaining the function of Mn atoms (2) and 23 and 16 kDa polypeptides are essential for functional stabilization of Cl− and Ca2+ (3). Ca2+ and Mn2+ are however, supposed to be ligated to the residual portion of the D1 and/or D2 polypeptide at the water splitting side of photosystem II (PSII) (4). The D1 polypeptide also named as 32 kDa protein of QB-protein is well known for its binding site of many herbicides on the acceptor side of PSII at the level of QB (5).