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تسجيل

Production of Acetyl-CoA (Activated Acetate):- Pyruvate Is Oxidized to Acetyl-CoA and CO2

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  p602-603

2026-06-06

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Production of Acetyl-CoA (Activated Acetate):- Pyruvate Is Oxidized to Acetyl-CoA and CO₂

The overall reaction catalyzed by the pyruvate dehydrogenase complex is an oxidative decarboxylation, an irreversible oxidation process in which the carboxyl group is removed from pyruvate as a molecule of CO₂ and the two remaining carbons become the acetyl group of acetyl-CoA (Fig. 16–2). The NADH formed in this re action gives up a hydride ion (:H^-) to the respiratory chain (Fig. 16–1), which carries the two electrons to oxygen or, in anaerobic microorganisms, to an alternative electron acceptor such as nitrate or sulfate. The transfer of electrons from NADH to oxygen ultimately generates 2.5 molecules of ATP per pair of electrons. The irreversibility of the PDH complex reaction has been demonstrated by isotopic labeling experiments: the complex cannot reattach radioactively labeled CO₂ to acetyl-CoA to yield carboxyl-labeled pyruvate.

FIGURE 16–2 Overall reaction catalyzed by the pyruvate dehydrogenase complex. The five coenzymes participating in this reaction, and the three enzymes that make up the enzyme complex, are discussed in the text.

FIGURE 16-3 Coenzyme A (CoA). A hydroxyl group of pantothenic acid is joined to a modified ADP moiety by a phosphate ester bond, and its carboxyl group is attached to β-mercaptoethylamine in amide linkage. The hydroxyl group at the 3position of the ADP moiety has a phosphoryl group not present in free ADP. The OSH group of the mercaptoethylamine moiety forms a thioester with acetate in acetyl coenzyme A (acetyl-CoA) (lower left).