Carbohydrate Metabolism I: Glycolysis and TCA Cycle
Steps involved in the decarboxylation and formation of the S-acetylhydrolipoyl enzyme of the dehydrogenase complex.
TPP = Thiamine pyrophosphate.
The structure of FAD that contains the vitamin riboflavin
is given in Figure 13-9. In the last step, catalyzed by di-
hydrolipoyl dehydrogenase, the hydrogens (or reducing
equivalents) are transferred to NAD+, with the formation
of NADH and the oxidized flavoprotein.
+ NAD+ ^ E3-FAD + NADH + H+
Thus, the flow of reducing equivalents in the pyruvate
dehydrogenase complex is from pyruvate to lipoyl to
FAD to NAD+. Conversion of pyruvate to acetyl-CoA
requires four vitamins: thiamine, pantothenic acid, ri-
boflavin, and niacin. In contrast, in glycolysis, niacin
is the only vitamin used. NADH generated in this re-
action is oxidized to NAD+ in the electron transport