Lipoic Acid (Lipoamide) as Acyl Carrier and Electron Carrier

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 FADH 2 and oxidized lipoamide (see Figure 14.10). Thus, lipoamide is both an electron carrier and an acyl group carrier.

See also: Pyruvate Dehydrogenase Complex, Lipoamide