The role of manganese in photosynthetic water oxidation

Summary The process of photosynthetic water oxidation to dioxygen under proton release takes place via a sequence of four univalent redox steps in a manganese-containing unit. In this mini-review the current state of knowledge is briefly described with special emphasis on the following topics: (a) the nature of the catalytic site, (b) the structure of the redox chemistry of the manganese-containing active site, (c) the ligand structure and the entry of substrate water into the redox cycle, and (d) problems of the stoichiometry of proton release coupled with individual redox steps and the possible role of other cofactors (Cl^–, Ca²⁺).