Mechanism of pyruvate decarboxylation by pyruvate decarboxylase- Pyruvate decarboxylase requires thiamine pyrophosphate (TPP) and Mg²⁺ as cofactors to catalyze decarboxylation reaction (Figure 7.3). Thiamine pyrophosphate is a co-enzyme present in pyruvate decarboxylase and responsible for stabilizing carbanion intermediate. The sequence of event of reaction catalyzed by pyruvate decarboxylase is as follows-

1. Deprotination of TPP to form TPP carbanion.
2. Carbanion attacks on carbonyl group of pyruvate to form adduct.
3. Release of CO₂ .
4. Resonance stabilization of intermediates.
5. Protonation to generate hydroxyl methyl TPP.
6. Release of acetaldehyde and regeneration of TPP from hydroxyl-TPP for next round of enzymatic catalysis.

Figure 7.3: Mechanistic details of conversion of pyruvate to acetaldehyde by pyruvate decarboxylase.