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The removal of the carboxyl group results in the emission of carbon dioxide during the decarboxylation process. A carbon atom from an organic molecule gets separated in this process.

The process involving reverse decarboxylation is catalysed by TPP (thiamine pyrophosphate). When a carbon-carbon bond connecting the carbonyl group to the reactive group, which is commonly a carboxylic acid or an alcohol present nearby, cleaves, reverse decarboxylation occurs.

TPP carbanion nucleophilically attacks the carbonyl group of the substrate. TPP attaches to the substrate by a single bond, breaking the substrate's target link. When a bond is broken, electrons are released, pushing them towards the TPP. This assists in the formation of a double bond between the TPP and the substrate. The electrons from the N-C double bond are forced into the nitrogen atom, reducing TPP to its neutral state.

The electrons are driven in the opposite way in reverse decarboxylase to build a carbon-hydrogen bond between the substrate and another atom. TPP is regenerated w1hen the TPP-substrate bond breaks.

The pyruvate decarboxylase has a prosthetic group called TPP. By functioning as the active site's core, it assists pyruvate decarboxylase in oxidising the substrate.