Open conformation of citrate synthase dimer complex with citrate (PDB code 1cts) and closed conformation of citrate synthase dimer complex with citrate and CoA (PDB code 2cts)
The Citric Acid Cycle (tricarboxylic acid cycle) is a series of enzyme catalyzed reactions which are critical in cellular respiration. Under oxidative conditions, pyruvate continues to be metabolized through the tricarboxylic acid cycle. In this cycle, Acetyl-CoA, a byproduct of glycolysis, along with various cofactors, are broken down into carbon dioxide, water, and energy in the form of GTP and NADH.
Pyruvate decarboxylation or pyruvate oxidation, also known as the link reaction (or oxidative decarboxylation of pyruvate), is the conversion of pyruvate into Acetyl-CoA by the enzyme complex pyruvate dehydrogenase complex (see Pyruvate dehydrogenase).
The multienzyme complex together catalyzes five distinct reactions in the conversion of pyruvate to Acetyl-CoA. The overall result is described by the following reaction:
Pyruvate + CoA + NAD+ ==> Acetyl-CoA + CO2 + NADH
However, pyruvate dehydrogenase (E1) is responsible for only the first two of the five reactions. The first of these is the decarboxylation of pyruvate and coupling of thiamine pyrophosphate (TPP) to form hydroxyethyl-TPP.
