Question

Are the reactions pyruvate to ethanol and pyruvate to lactate both reversible. If not, why not?

Answer 1

The pyruvate → lactate reaction is reversible, but the pyruvate → ethanol reaction is irreversible.

In homolactic fermentation, pyruvate is reversibly reduced to lactate o regenerate NAD⁺. In alcoholic fermentation, pyruvate is decarboxylated by a thiamine pyrophosphate (TPP)–dependent mechanism, to yield CO₂ and acetaldehyde, which is then reduced by NADH to yield NAD⁺ and ethanol.