Water, four-electron dioxygen reduction metal ions

The reduced species Fe2+ and Mn2+ have been detected electrochemically in anoxic waters (De Vitre et al., 1988). Vanadyl (V02 + ) is known to be incorporated in geoporphyrins in organic-rich sediments (Eckstrom et al., 1983). Moffett and Zika (1988) measured reduced Cu(I) photometrically in surface waters of the open ocean. The oxidation of these four metal species involves a simple one-electron transfer step. Haber and Weiss (1934) proposed a kinetic mechanism for the oxygenation of the ferrous ion, in which the first step in the four-electron reduction of the dioxygen molecule determines the rate. The redox potentials for the corresponding oxygen couples support this view they are plotted ill... 

Structure and Mechanism. Cytochrome-c oxidase catalyzes the four-electron reduction of molecular oxygen to water and couples these redox processes to proton transfer across the mitochondrial membrane.As depicted in Fig. 24, the enzyme is structurally complex and contains four metal centers which are redox active, two copper ions and two heme a groups. One copper ion, Cug, and one of the heme a groups, cytochrome <13, (cyt a ), form a binuclear center which binds dioxygen. Electrons are ... 

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