would be the last sugar fermented in this mixture. Depending on how the cells had previously been grown, however, it is possible that invertase had already been induced, resulting in rapid formation of sucrose hydrolysis products. Finally, there exist strains of S. cerevisiae whose expression of cata-bolic genes is constitutive, meaning that they are not subject to catabolite repression. Such strains may be particularly useful, since constitutive expression of genes coding for maltose permease and maltase means that these strains will ferment maltose even in the presence of glucose. In most doughs, however, glucose is metabolized rather quickly, and the maltose utilization genes would soon be de-repressed and induced, even in non-constitutive strains.
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