title: Quantum chemical studies of manganese centers in biology.
abstract: During the past five years, hybrid density functional theory has been used to study mechanisms for redox-active enzymes containing complexes with a variety of different transition metals. In this paper, suggested mechanisms of some manganese enzymes are described. For photosystem II, a mechanism is proposed leading to an oxyl radical in the S(3)-state, which is the precursor for the O-O bond formation. For manganese catalase, the suggested mechanism instead leads to the formation of a hydroxyl radical after the O-O bond of hydrogen peroxide is cleaved. This radical is immediately quenched by a manganese center. Parallels between these enzymes are highlighted. Jahn-Teller and trans effects are emphasized.
authors.affiliation: Department of Physics, Stockholm Center for Physics, Astronomy and Biotechnology (SCFAB), Stockholm University, S-106 91, Stockholm, Sweden. ps@physto.se
authors.forename: Per E M
authors.initials: PE
authors.lastname: Siegbahn
mesh_terms: D001665:Binding Sites; D004798:Enzymes / Q000737:chemistry; D008345:Manganese / Q000737:chemistry*; D008667:Metalloproteins / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry; D045332:Photosystem II Protein Complex; D011789:Quantum Theory
chemical_list: D004798:Enzymes; D008667:Metalloproteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D008345:Manganese