Mechanism of Action of PDH Complex

 A : pyruvate decarboxylase - thiamine pyrophosphate
         TPP removes COOH from pyruvate leaving
         2 carbon fragment that binds the acyl
         fragment to the S-TPP.

 B : lipomide reductase transacetylase - lipoate
         2 carbon acyl group is transferred  to one
         lipoamide arm, and then to the other,
         to position it for CoASH transfer.

 C : dihydrolipoyl dehydrogenase- CoASH, FAD, NAD+
         acyl group is transferred to CoASH;
         the reduced lipoamides transfers 
         2H's to E-FAD -->  E-FADH2,  and then
         E-FADH2 passes H to NAD+ --> NADH