Selection of Mutants Increasing the Rate of Fermentation in Yeast. Progress Report

摘要

Mitochondrial transport mechanisms were found to be responsible for the regulation of an isozyme of yeast alcohol dehydrogenase (ADH) and possibly other cellurlar processes. Two ADH isozymes from Zymomonas mobilis were characterized. They were found to be markedly different from each other. One, a tetramer, has a subunit molecular weight very close to those of yeast and mammalian ADH's and its kinetics and other properties are also very similar. The other, a dimer, has a markedly smaller subunit molecular weight and strains can be established in which this isozyme is lost, suggesting that it may be on a plasmid. This isozyme also has markedly different kinetics, particularly a very large K/sub m/ for ethanol suggesting that its primary substrate may not in fact be ethanol. Five functional mutants of yeast alcohol dehydrogenase were localized that affect its kinetics without destroying its function. These mutants are scattered widely through the catalytic domain of the enzyme subunit, and while two can be related in a direct way to the altered enzyme function the other three cannot. All the mutational changes which have been determined so far involve the substitution of an arginine for another amino acid.