title: Pyruvate decarboxylase catalyzes decarboxylation of branched-chain 2-oxo acids but is not essential for fusel alcohol production by Saccharomyces cerevisiae.
abstract: The fusel alcohols 3-methyl-1-butanol, 2-methyl-1-butanol, and 2-methyl-propanol are important flavor compounds in yeast-derived food products and beverages. The formation of these compounds from branched-chain amino acids is generally assumed to occur via the Ehrlich pathway, which involves the concerted action of a branched-chain transaminase, a decarboxylase, and an alcohol dehydrogenase. Partially purified preparations of pyruvate decarboxylase (EC 4.1.1.1) have been reported to catalyze the decarboxylation of the branched-chain 2-oxo acids formed upon transamination of leucine, isoleucine, and valine. Indeed, in a coupled enzymatic assay with horse liver alcohol dehydrogenase, cell extracts of a wild-type Saccharomyces cerevisiae strain exhibited significant decarboxylation rates with these branched-chain 2-oxo acids. Decarboxylation of branched-chain 2-oxo acids was not detectable in cell extracts of an isogenic strain in which all three PDC genes had been disrupted. Experiments with cell extracts from S. cerevisiae mutants expressing a single PDC gene demonstrated that both PDC1- and PDC5-encoded isoenzymes can decarboxylate branched-chain 2-oxo acids. To investigate whether pyruvate decarboxylase is essential for fusel alcohol production by whole cells, wild-type S. cerevisiae and an isogenic pyruvate decarboxylase-negative strain were grown on ethanol with a mixture of leucine, isoleucine, and valine as the nitrogen source. Surprisingly, the three corresponding fusel alcohols were produced in both strains. This result proves that decarboxylation of branched-chain 2-oxo acids via pyruvate decarboxylase is not an essential step in fusel alcohol production.
authors.affiliation: Department of Molecular Cell Biology, Utrecht University, The Netherlands.
authors.forename: E G
authors.initials: EG
authors.lastname: ter Schure
authors.forename: M T
authors.initials: MT
authors.lastname: Flikweert
authors.forename: J P
authors.initials: JP
authors.lastname: van Dijken
authors.forename: J T
authors.initials: JT
authors.lastname: Pronk
authors.forename: C T
authors.initials: CT
authors.lastname: Verrips
mesh_terms: D000426:Alcohol Dehydrogenase / Q000378:metabolism; D000438:Alcohols / Q000378:metabolism*; D000818:Animals; D003653:Decarboxylation; D005421:Flavoring Agents; D005524:Food Technology; D006736:Horses; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology; D011767:Pyruvate Decarboxylase / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000438:Alcohols; D005421:Flavoring Agents; C007807:fusel oil; D000426:Alcohol Dehydrogenase; D011767:Pyruvate Decarboxylase