α,β-Dicarbonyl reduction is mediated by the Saccharomyces Old Yellow Enzyme

• Published in: FEMS yeast research 2016-08, Vol.16 (5), p.fow059
• Main Authors: van Bergen, Barry, Cyr, Normand, Strasser, Rona, Blanchette, Maxime, Sheppard, John D., Jardim, Armando
• Format: Article
• Language: English
• Subjects: Acetoin - metabolism; Diacetyl - metabolism; Gene Expression Profiling; Kinetics; Mass Spectrometry; NADP - metabolism; NADPH Dehydrogenase - isolation & purification; NADPH Dehydrogenase - metabolism; Oxidation-Reduction; Pentanones - metabolism; Saccharomyces cerevisiae - enzymology; Saccharomyces cerevisiae - metabolism
• ISSN: 1567-1364; 1567-1364
• DOI: 10.1093/femsyr/fow059

The undesirable flavor compounds diacetyl and 2,3-pentanedione are vicinal diketones (VDKs) formed by extracellular oxidative decarboxylation of intermediate metabolites of the isoleucine, leucine and valine (ILV) biosynthetic pathway. These VDKs are taken up by Saccharomyces and enzymatically converted to acetoin and 3-hydroxy-2-pentanone, respectively. Purification of a highly enriched diacetyl reductase fraction from Saccharomyces cerevisiae in conjunction with mass spectrometry identified Old Yellow Enzyme (Oye) as an enzyme capable of catalyzing VDK reduction. Kinetic analysis of recombinant Oye1p, Oye2p and Oye3p isoforms confirmed that all three isoforms reduced diacetyl and 2,3-pentanedione in an NADPH-dependent reaction. Transcriptomic analysis of S. cerevisiae (ale) and S. pastorianus (lager) yeast during industrial fermentations showed that the transcripts for OYE1, OYE2, arabinose dehydrogenase (ARA1), α-acetolactate synthase (ILV2) and α-acetohydroxyacid reductoisomerase (ILV5) were differentially regulated in a manner that correlated with changes in extracellular levels of VDKs. These studies provide insights into the mechanism for reducing VDKs and decreasing maturation times of beer which are of commercial importance. The authors have identified and characterized Old Yellow Enzyme as an enzyme capable of reducing the undesirable beer flavor compound diacetyl in an NADPH-dependent reaction. Graphical Abstract Figure. The authors have identified and characterized Old Yellow Enzyme as an enzyme capable of reducing the undesirable beer flavor compound diacetyl in an NADPH-dependent reaction.