Functional mutants of yeast alcohol dehydrogenase

Selection of petite strains of yeast (that is, strains unable to respire aerobically) on media containing allyl alcohol will result in enrichment for mutants at the ADC1 locus. This locus codes for the constitutive alcohol dehydrogenase, ADH-I, which is primarily responsible for the production of ethanol in yeast. The mutant enzymes are functional, and confer resistance to allyl alcohol on the cell by shifting the NAD-NADH balance in the direction of NADH. These mutants exhibit altered Km's for cofactor, substrate, or both, and often have altered Vmax's. In this paper, the methodology for obtaining these mutants and for determining the amino acid substitutions responsible for these changes is presented. Several new mutants have been at least approximately localized, and one, DB-AA3-N15, has been shown to be due to the substitution of an arginine for a tryptophan at position 54. This substitution would be expected, by analogy with the known tertiary structure of the horse liver alcohol dehydrogenase, to decrease the hydrophobic environment of the active site pocket. The substitution has a pronounced effect on the Km for ethanol, but far less on that for acetaldehyde. The current status of investigation of other classes of functional mutants of this enzyme, and the potential both for selection of useful variants of this molecule and for an increase understanding of its function are discussed.