Major of three pyruvate decarboxylases (PDC1, PDC5, PDC6) implicated in the nonoxidative conversion of pyruvate to acetaldehyde and carbon dioxide during alcoholic fermentation. Most of the produced acetaldehyde is subsequently reduced to ethanol, but some is required for cytosolic acetyl-CoA production for biosynthetic pathways. The enzyme is also one of five 2-oxo acid decarboxylases (PDC1, PDC5, PDC6, ARO10, and THI3) able to decarboxylate more complex 2-oxo acids (alpha-ketoacids) than pyruvate, which seem mainly involved in amino acid catabolism. Here the enzyme catalyzes the decarboxylation of amino acids, which, in a first step, have been transaminated to the corresponding 2-oxo acids. In a third step, the resulting aldehydes are reduced to alcohols, collectively referred to as fusel oils or alcohols. Its preferred substrates are the transaminated amino acids derived from threonine (2-oxobutanoate), norvaline (2-oxopentanoate), valine (3-methyl-2-oxobutanoate, also alpha-keto-isovalerate), isoleucine ((3S)-3-methyl-2-oxopentanoate, also alpha-keto-beta-methylvalerate), phenylalanine (phenylpyruvate), and tryptophan (3-(indol-3-yl)pyruvate), whereas transaminated leucine is no substrate. In a side-reaction the carbanionic intermediate (or active aldehyde) generated by decarboxylation or by activation of an aldehyde can react with an aldehyde via condensation (or carboligation) yielding a 2-hydroxy ketone, collectively called acyloins. H(+) + pyruvate = acetaldehyde + CO2 3-methyl-2-oxobutanoate + H(+) = 2-methylpropanal + CO2 (S)-3-methyl-2-oxopentanoate + H(+) = 2-methylbutanal + CO2 H(+) + indole-3-pyruvate = CO2 + indole-3-acetaldehyde 3-phenylpyruvate + H(+) = 2-phenylacetaldehyde + CO2 2-oxobutanoate + H(+) = CO2 + propanal 2-oxopentanoate + H(+) = butanal + CO2 2 acetaldehyde = acetoin acetaldehyde + H(+) + pyruvate = acetoin + CO2 Binds 1 Mg(2+) per subunit. Binds 1 thiamine pyrophosphate per subunit. Allosterically activated by its substrate, pyruvate. Fermentation; ethanol fermentation. Amino-acid degradation; Ehrlich pathway. Homotetramer. Protein expression is strongly induced by high concentrations of fermentable carbon sources and under anaerobic growth conditions and is repressed by ethanol. Protein expression level is also autoregulated through an unknown mechanism. Cleavage of N-terminal methionine and N-terminal acetylation by NAT1/ARD1. Fusel oils and acyloins are important flavor and aroma compounds in yeast-fermented products contributing to the quality of beverages and food, e.g. fusel oils in whiskey, contrary to common believe, seem to alleviate hangover. In general they are desirable at low concentrations, whereas high concentrations may spoil the product. By adjusting growth conditions and substrate their production is sought to be influenced. Due to their broad substrate tolerance pyruvate decarboxylases are important biocatalysts for chemoenzymatic syntheses, both by fermentation and in vitro, e.g. in the production of ephedrine, vitamin E, or phenylethanol (rose flavor). Present with 8966 molecules/cell in log phase SD medium. Belongs to the TPP enzyme family.