Succinate dehydrogenase

Succinate dehydrogenase oxidizes succinate to fumarate and transfers the electrons through bound cofactors to ubiquinone. In mitochondria it is respiratory complex II, linking the citric acid cycle with the respiratory chain.

Unlike complexes I, III, and IV, it does not itself pump protons across the membrane. This distinction explains why electrons entering through succinate contribute differently to the proton-motive output than electrons entering through NADH.