Saccharomyces cerevisiae NADH dehydrogenase

Fig. 1. Redox metabolism in Saccharomyces cerevisiae during anaerobic growth on glucose. The ethanol yield is lowered by the production of biomass and glycerol. The glycerol flux, x, can be decreased, and the ethanol yield thereby increased if the stoichiometric coefficient a for biomass formation is reduced, e.g., by having nitrogen assimilation via an NADH-depen-dent glutamate dehydrogenase [10]...

The NADH dehydrogenase of yeast is of considerable interest because in Saccharomyces cerevisiae and Saccharomyces carlsbergensis coupling site 1 is absent, whereas in Candida utilis its existence depends on the growth phase of the cells and can be altered by adaptations to culture conditions and by catabolite repression. 

Pyruvate is initially decarboxylated into ethanal by pyruvate decarboxylase. This enzyme needs magnesium and thiamine pyrophosphate as cofactors (Hohmann 1996). Thereafter, alcohol dehydrogenase reduces ethanal to ethanol, recycling the NADH to NAD+. There are three isoenzymes of alcohol dehydrogenase in Saccharomyces cerevisiae, but isoenzyme I is chiefly responsible for converting ethanal into ethanol (Gancedo 1988). Alcohol dehydrogenase uses zinc as cofactor (Ciriacy 1996). 

A narrow substrate spectrum has been described for tiie yeast alcohol dehydrogenase (YADH) from Saccharomyces cerevisiae, making it a suitable biocatalyst only for molecules like methanol, ethanol, or in some cases acetone. Unfortunately the cofactor NADH is needed, which is regenerated by FDH (Scheme 29.6c). For the asymmetric synthesis of (S)-phenylethylamine with isopropylamine (IPA) as amino donor, acetone was converted to isopropyl alcohol catalyzed by YADH. The effectiveness of this method was compared to the reaction without YADH/FDH. A conversion yield of 99% was achieved with the YADH/FDH system while a conversion yield of 63-89% was obtained without YADH/FDH [69]. 

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