Question Detail

Cytochrome c oxidase (Complex IV) is the last enzyme in the electron transport chain. It contains two heme groups (with iron) and two copper centers (CuA and CuB). The copper ions are essential for its function in transferring electrons to oxygen. The question might be expecting Copper (Cu) as a key distinguishing metal, though iron is also present. In many introductory contexts, cytochrome oxidase is highlighted for its copper content. Option A is Fe (Iron). Option E is Cu (Copper). Since it contains both, but Cu is more specific to this complex's description in some texts, and CN (cyanide) is an inhibitor, not a component. The best single answer is E. Cu.