E2 is a catalytic activity found in the pyruvate dehydrogenase complex. It forms the core of the complex. 24 copies of E2 are found in the complex isolated from Azotobacter. E2 is covalently bound to lipoic acid, forming lipoamide. Lipoamide functions to oxidize the aldehyde moiety transferred to it from E1 to an acetyl group and to subsequently transfer it to coenzyme A, forming acetyl-CoA. Electrons from E2 are, in turn, passed to FAD, in a reaction catalyzed by E3.

-Keto Acid Complexes - A Review