INVOLVEMENT OF CARBOXYL GROUPS OF THE PSII REACTION-CENTER PROTEINS IN PHOTOACTIVATION OF THE APO-WATER-OXIDIZING COMPLEX

Involvement of residues of acidic amino acids in photo-ligation of man ganese into the ape-water-oxidizing complex was investigated by use of 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC), a water-solubl e carboxyl modifier. Treatment of Mn-depleted PSII membranes by EDC in the presence of nucleophiles induced a loss of photoactivation capabi lity in the Mn complex and partial loss of capability of photooxidatio n of Mn2+, but little decrease in the DCIP photoreduction supported by diphenylcarbazide. The inhibition of diphenylcarbazide-photooxidation by submicromolar Mn2+, indicative of the intactness of high-affinity Mn-binding sites, was apparently abolished by EDC treatment. From amin o acid quantitation analysis of D1 and D2 proteins and CP47 of the che mically-modified membranes, approximately three carboxyl groups of the D1 protein were found to be chemically-modified with EDC after remova l of the functional Mn. These results suggest that acidic amino acids on the D1 protein are involved in photoactivation of the ape-water-oxi dizing complex and probably in ligation of Mn to the water-oxidizing c omplex.