Succinate dehydrogenase is an enzyme that catalyzes the conversion of succinate to fumarate in the tricarboxylic acid (TCA) cycle, also known as the Krebs cycle or citric acid cycle. This reaction is important for the generation of energy in the form of ATP through oxidative phosphorylation.
The reaction catalyzed by succinate dehydrogenase is as follows:
Succinate + FAD -> Fumarate + FADH2
In this reaction, succinate is oxidized to fumarate, and FAD (flavin adenine dinucleotide) is reduced to FADH2. The electrons removed from succinate are transferred to the FAD cofactor, which is bound to the enzyme, and are ultimately passed on to the electron transport chain to generate ATP.
Succinate dehydrogenase differs from malate dehydrogenase, another enzyme in the TCA cycle, in several ways. First, succinate dehydrogenase is a membrane-bound enzyme, located in the inner mitochondrial membrane, while malate dehydrogenase is a soluble enzyme located in the mitochondrial matrix.
Second, succinate dehydrogenase uses FAD as a cofactor, while malate dehydrogenase uses NAD+. FAD is a lower-potential electron acceptor than NAD+, which means that the reaction catalyzed by succinate dehydrogenase generates less ATP than the reaction catalyzed by malate dehydrogenase.
Finally, succinate dehydrogenase catalyzes a reaction in which succinate is oxidized to fumarate, while malate dehydrogenase catalyzes a reaction in which malate is oxidized to oxaloacetate. These reactions are both important for the TCA cycle and for the generation of ATP through oxidative phosphorylation.