Malonate is a classic competitive inhibitor of succinate dehydrogenase — the enzyme that catalyses the oxidation of succinate to fumarate in the TCA cycle (Complex II of the electron transport chain). Malonate is structurally similar to succinate (both are dicarboxylic acids) and competes for the active site without being oxidised. This competitive inhibition is reversible by increasing succinate concentration. This is one of the most cited examples of competitive inhibition in biochemistry.