The oxoglutarate dehydrogenase complex (OGDC) or α-ketoglutarate dehydrogenase complex is an enzyme complex, most commonly known for its role in the citric acid cycle. The oxoglutarate dehydrogenase complex (OGDC) or α-ketoglutarate dehydrogenase complex is an enzyme complex, most commonly known for its role in the citric acid cycle. Much like pyruvate dehydrogenase complex (PDC), this enzyme forms a complex composed of three components: Three classes of these multienzyme complexes have been characterized: one specific for pyruvate, a second specific for 2-oxoglutarate, and a third specific for branched-chain α-keto acids. The oxoglutarate dehydrogenase complex has the same subunit structure and thus uses the same coenzymes as the pyruvate dehydrogenase complex and the branched-chain alpha-keto acid dehydrogenase complex (TTP, CoA, lipoate, FAD and NAD). Only the E3 subunit is shared in common between the three enzymes.