Which enzyme is responsible for the function of complex 2 in the Electron Transport Chain?

The enzyme responsible for the function of complex II in the Electron Transport Chain is succinate dehydrogenase. This enzyme plays a dual role; it is involved in both the citric acid cycle and the electron transport chain. In the citric acid cycle, succinate dehydrogenase catalyzes the conversion of succinate to fumarate, simultaneously reducing FAD to FADH2. The FADH2 produced then enters the electron transport chain at complex II, where it donates electrons.

Complex II is unique compared to other complexes in the electron transport chain, as it does not pump protons across the mitochondrial membrane and instead contributes to the overall electron flow directly from succinate (via FADH2) to ubiquinone (coenzyme Q), which then passes the electrons to complex III. This process emphasizes the central role of succinate dehydrogenase not only in the Krebs cycle but also in facilitating electron transfer, underscoring its essential function within the electron transport chain.

The other options represent different enzymes or complexes with distinct roles: citrate synthase is involved in the formation of citrate from acetyl-CoA and oxaloacetate, ubiquinone oxidoreductase (which is essentially complex I)