Is succinate dehydrogenase a part of the citric acid cycle or the electron transport chain?

Succinate dehydrogenase plays a unique and pivotal role at the intersection of the citric acid cycle and the electron transport chain. In the citric acid cycle, it catalyzes the conversion of succinate to fumarate, during which it also facilitates the reduction of coenzyme Q (ubiquinone) to ubiquinol, effectively transferring electrons. This dual functionality is what allows succinate dehydrogenase to be categorized as both a component of the citric acid cycle and a part of the electron transport chain.

In the context of the citric acid cycle, this enzyme is essential for the continuation of the cycle by ensuring a constant supply of fumarate for subsequent reactions. Simultaneously, by contributing to the electron transport chain, it aids in the process of oxidative phosphorylation, where the electrons are ultimately used for ATP production. This interconnectedness reinforces the importance of succinate dehydrogenase in cellular metabolism, demonstrating its role as a key enzyme bridging two major biochemical pathways.