Abstract
Cells of the wildtype yeast strain Zygosaccharomyces bisporus CBS 702 form αhydroxy ketones from aromatic amino acid precursors during fermentation. Pyruvate decarboxylase (PDC, E.C. 4.1.1.1), the key enzyme of this biotransformation catalysing the nonoxidative decarboxylation of pyruvate and other 2- oxoacids, was purified and characterised. The active enzyme is homotetrameric (α[4]) with a molecular mass of about 244 kDa. Activation of PDC by its substrate pyruvate results in a sigmoidal dependence of the reaction rate from substrate concentration (apparent K value 1.73 m; Hill coefficient 2.10). A cDNA library was screened using a PCRbased procedure, and a 1856 bp cDNA of PDC was identified and sequenced. The cDNA encodes a polypeptide of 563 amino acid residues (monomeric unit). Sequence alignments demonstrate high homologies ([greater than] 80%) to PDC genes from Saccharomyces cerevisiae, Kluyveromyces lactis and Kluyveromyces marxianus.
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