Modification of Photosystem II by phenylglyoxal. Evidence for the involvement of arginine in atrazine binding to chloroplasts

Shipman [(1981) J. Theor. Biol. 90, 123-148] has recently noted that herbicides from various chemical classes which inhibit electron transport through Photosystem II have a flat polar component in the range 3-5 debye, and he suggests that this component of the herbicide interacts with a strong electric field across the protein binding site in the thylakoid. This polar portion of the binding site could be a salt bridge, the cationic end of which may be an arginine residue. Phenylglyoxal is a protein-modifying reagent with specificity toward arginine residues. Pretreatment of chloroplast membranes with 50 mM phenylglyoxal for 30 min at 30°C completely abolished the ability to bind specifically [¹⁴C]atrazine. Pretreatment with 50 mM phenylglyoxal also completely abolished the subsequent ability of the chloroplasts to carry out photosynthetic electron transport. These data provide strong evidence for the involvement of arginine residues in the binding and action of Photosystem II herbicides.