In the pyruvate dehydrogenase complex, the carboxyl group of lipoic acid is covalently attached to a lysine- amino group of dihydrolipoamide transacetylase enzyme, forming lipoamide.

Lipoamide accepts the activated aldehyde produced by the TPP-mediated decarboxylation. As the activated aldehyde is bound, it donates electrons to reduce the oxidized disulfide bond of lipoamide, forming a sulfhydryl and an acetyl-group bound to the other sulfur.

Subsequently the acetyl group is passed to CoASH, forming acetyl-CoA and fully reduced lipoamide.

In the last step of pyruvate oxidation, lipoamide transfers electrons to FAD, forming FADH2 and oxidized lipoamide (see Figure 14.10). Thus, lipoamide is both an electron carrier and an acyl group carrier.