Electron and proton transfer in cytochrome c oxidase

Sammanfattning: This doctoral thesis describes results from studies on the mechanisms by which the enzyme cytochrome c oxidase catalyses the reduction of oxygen to water. Cytochrome c oxidase is the last integral enzyme complex of the socalled respiratory chain in the mitochondrial inner membrane (plasma membrane of bacteria). The reaction catalysed by cytochrome c oxidase produces a charge separation across the membrane by two separate mechanisms. The protons and the electrons needed to reduce oxygen to water are supplied from different sides of the membrane, and the energy released in this reaction is used by cytochrome c oxidase to pump protons against the electro-chemical gradient across the membrane. Another integral enzyme, ATP-synthase, utilises this gradient for synthesis of ATP, which in turn is used in many of the energyrequiring processes of a cell. Cytochrome c oxidase holds four redox-active metal centres that mediate electron transfer to, and reduction of the O2-molecule. One part of the thesis concerns the rates of electron transfer as well as the redox equilibrium between the metal sites (papers II and IV).Since the oxygen chemistry takes place in the membrane-spanning part of the enzyme it is equipped with two proton-transfer pathways that lead from the bulk solution to the active site. A second part of the thesis concerns the location of the entry-point of one of these pathways as well as the role of this pathway during the catalytic cycle (papers I and III).The third part of the thesis concerns the mechanism by which the enzymecouples the O2-chemistry to proton pumping (paper V).