Molecular and physiological aspects of alcohol dehydrogenases in the ethanol metabolism of Saccharomyces cerevisiae

Authors

  • Olga de Smidt,

    1. Department of Microbial, Biochemical & Food Biotechnology, University of the Free State, Bloemfontein, South Africa
    2. School of Agriculture and Environmental Sciences, Central University of Technology, Bloemfontein, South Africa
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  • James C. du Preez,

    1. Department of Microbial, Biochemical & Food Biotechnology, University of the Free State, Bloemfontein, South Africa
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  • Jacobus Albertyn

    Corresponding author
    • Department of Microbial, Biochemical & Food Biotechnology, University of the Free State, Bloemfontein, South Africa
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Correspondence: Jacobus Albertyn, Department of Microbial, Biochemical & Food Biotechnology, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa. Tel.: +27 51 401 2223; fax: +27 51 401 9379; e-mail: Albertynj@ufs.ac.za

Abstract

The physiological role and possible functional substitution of each of the five alcohol dehydrogenase (Adh) isozymes in Saccharomyces cerevisiae were investigated in five quadruple deletion mutants designated strains Q1–Q5, with the number indicating the sole intact ADH gene. Their growth in aerobic batch cultures was characterised in terms of kinetic and stoichiometric parameters. Cultivation with glucose or ethanol as carbon substrate revealed that Adh1 was the only alcohol dehydrogenase capable of efficiently catalysing the reduction of acetaldehyde to ethanol. The oxidation of produced or added ethanol could also be attributed to Adh1. Growth of strains lacking the ADH1 gene resulted in the production of glycerol as a major fermentation product, concomitant with the production of a significant amount of acetaldehyde. Strains Q2 and Q3, expressing only ADH2 or ADH3, respectively, produced ethanol from glucose, albeit less than strain Q1, and were also able to oxidise added ethanol. Strains Q4 and Q5 grew poorly on glucose and produced ethanol, but were neither able to utilise the produced ethanol nor grow on added ethanol. Transcription profiles of the ADH4 and ADH5 genes suggested that participation of these gene products in ethanol production from glucose was unlikely.

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