One of five 2-oxo acid decarboxylases (PDC1, PDC5, PDC6, ARO10, and THI3) involved in amino acid catabolism. The enzyme catalyzes the decarboxylation of amino acids, which, in a first step, have been transaminated to the corresponding 2-oxo acids (alpha-keto-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 leucine (4-methyl-2-oxopentanoate, also alpha-keto-isocaproate) and isoleucine ((3S)-3-methyl-2-oxopentanoate, also alpha-keto-beta-methylvalerate), whereas transaminated valine, transaminated aromatic amino acids, and pyruvate are no substrates. In analogy to the pyruvate decarboxylases the enzyme may in a side-reaction catalyze condensation (or carboligation) reactions leading to the formation of 2-hydroxy ketone, collectively called acyloins. The enzyme is also positively regulating the thiamine metabolism by a molecular mechanism that may involve thiamine concentration sensing and signal transmission. 4-methyl-2-oxopentanoate + H(+) = 3-methylbutanal + CO2 (S)-3-methyl-2-oxopentanoate + H(+) = 2-methylbutanal + CO2 Binds 1 Mg(2+) per subunit. Binds 1 thiamine pyrophosphate per subunit. Amino-acid degradation; Ehrlich pathway. Fusel oils are important flavor and aroma compounds in yeast-fermented products contributing to the quality of beverages and food. In low concentration they are generally desirable, whereas high concentrations may spoil the product. By adjusting growth conditions and substrate their production is sought to be influenced. Present with 2140 molecules/cell in log phase SD medium. Belongs to the TPP enzyme family. While genetic evidence suggests this enzyme is involved in leucine and isoleucine catabolism (PubMed:9341119, PubMed:10753893), no decarboxylase enzymatic activity could be detected in cell extracts of S.cerevisiae strains expressing the individual gene (PubMed:22904058). Truncated N-terminus.