Metal centers of cytochrome c oxidase: structures and interactions

Studies directed toward the elucidation of the structures of the metal centers in cytochrome c oxidase are reviewed. Progress towards an understanding of the interactions between these centers and their spatial distributions within the protein will also be presented. Our studies are based primarily on optical and low-temperature electron paramagnetic resonance (EPR) spectroscopy. We have employed nitric oxide (NO), as well as other exogenous ligands, to probe the 0 2 reduction site of the enzyme. In addition, we have isolated auxotrophs of Saccharomyces cerevisiae in order to metabolically incorporate isotopically substituted amino acids into the ye double resonance (ENDOR) spectroscopic studies of these isotopically substituted derivatives have provided unambiguous information on the structure of two of the four metal centers. The degree to which metal centers within the protein interact with one another has been assessed by examining the extent to which redox changes of one metal center modulate changes in the EPR and optical characteristics of the other centers. Conceptions about the overall spatial distribution of the metal centers within the protein emerge from these data. The implications of our results with respect to the mechanisms of dioxygen reduction and energy conservation in cytochrome c oxidase will be discussed.