21] Ligands of cytochrome c oxidase

Abstract

Publisher Summary This chapter discusses the ligands of cytochrome c oxidase. There are four oxidation–reduction components in cytochrome c oxidase and most of the ligands discussed in the chapter bind to one or more of these components. Current knowledge of the reactivity of the four components toward added ligands indicates that the “visible” copper is unreactive, whereas cytochrome a 3 is readily accessible to and binds many ligands. Because the reduced cytochrome a 3 -cyanide complex is rapidly oxidized by molecular oxygen, the inhibition thus appears to occur through formation of the reduced cytochrome a 3 -cyanide complex, which is then oxidized to the more stable oxidized cytochrome a 3 -cyanide complex. A general observation for the cyanide inhibition is that the cyanide inhibitor constant is greater than the dissociation constant for cyanide from the oxidized cytochrome c oxidase, but smaller than the cyanide dissociation constant from the reduced oxidase.