Enzyme converting pyruvate to acetaldehyde in ethanol fermentation is:
Alcoholic fermentation in Saccharomyces cerevisiae and Zymomonas mobilis proceeds through an expanded glycolytic branch after pyruvate formation. Pyruvate decarboxylase, a thiamine pyrophosphate-dependent homotetramer encoded by PDC1, PDC5, PDC6, binds Mg2+ and performs non-oxidative decarboxylation of pyruvate to acetaldehyde and carbon dioxide. Mechanistically, TPP ylide attacks carbonyl carbon forming lactyl-TPP, decarboxylates to hydroxyethyl-TPP carbanion, then releases acetaldehyde and regenerates ylide. This irreversible, highly exergonic step commits carbon toward ethanol and prevents
Ref: Lehninger Principles of Biochemistry 8th ed. Ch 14; Nature Scientific Reports 2022 PDC mechanism https://www.nature.com/articles/s41598-022-08568-4