Glucose catabolic repression

Since more ATP is produced by respiration of glucose than by fermentation, and since the ATP requirement for biosynthesis of cell mass is the same, it follows that to obtain the same cell yield from glucose, the yeast should consume less sugar under aerobic conditions than under anaerobic conditions, with a resultant decrease in glycolytic flux (Berry, 1982). These phenomena are referred to as the Pasteur effect. Although this effect is observed in some yeasts, in S. cerevisiae it is either absent (Gancedo and Serrano, 1989) or observed only under certain nutrient-limited conditions. The main reason for the absence of the Pasteur effect is that even under aerobic conditions, fermentation is still the main catabolic route for the utilisation of glucose because of the Crabtree effect (Walker, 1994). The Crabtree effect is the repression... 

Catabolite repression. The general repression of transcription of genes associated with catabolism that is seen in the presence of glucose. 

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