2-oxoglutarate dehydrogenase is a key enzyme in the TCA cycle, converting 2-oxoglutarate, coenzyme A and NAD(+) to succinyl-CoA, NADH and carbon dioxide [PMID:16321804]. This activity of this enzyme is tightly regulated and it is a major determinant of the metabolic flux through the TCA cycle. This enzyme is composed of multiple copies of three different subunits: 2-oxoglutarate dehydrogenase (E1), dihydrolipoamide succinyltransferase (E2) and lipoamide dehydrogenase (E3) which is often shared with similar enzymes such as pyruvate dehydrogenase [PMID:9278141]. The E2 component forms a large multimeric core which binds the peripheral E1 and E3 subunits. The substrate is transferred between the active sites of the different subunits by a lipoyl moiety, bound to a lysine residue from the E2 polypeptide.

This entry represents the E1 subunit of 2-oxoglutarate dehydrogenase. It catalyses the decarboxylation of this compound in a thiamine pyrophosphate-dependent manner, transferring the resultant succinyl group onto the liposyl moiety bound to the E2 subunit. The E1 ortholog from Corynebacterium glutamicum is unusual in having an N-terminal extension that resembles the E2 component of 2-oxoglutarate dehydrogenase enzyme.