The His332 residue of the D1 protein has been identified as the likely ligand of the catalytic Mn ions in the water oxi-dizing complex (Ferreira, ., Iverson, ., Maghlaoui, K., Barber, J. & Iwata, S. (2004) Science303, 1831–1838). However, its function has not been fully clarified. Here we used thermoluminescence and flash-induced chlorophyll fluorescence measurements to characterize the effect of theD1-H333E,D1-H332DandD1-H332Smutationson the electron transport of Photosystem II in intact cells of the cyanobacteriumSynechocystis6803
