Ethanol yield by Saccharomyces cerevisiae in very high glucose (VHG) media with an amino acid supplement was investigated. Amino acid supplementation led to positive cell responses, including reduced lag time and increased cell viability in VHG media. A quantitative shotgun proteomic analysis was used to understand how amino acid supplemented S. cerevisiae responds to high osmotic conditions. iTRAQ data revealed that most proteins involved in glycolysis and pentose phosphate pathways were up-regulated under high glucose shock. Reactivation of amino acid metabolism was also observed at the end of the lag phase. The relative abundance of most identified proteins, including aminoacyl-tRNA biosynthesis proteins, and heat-shock proteins, remained unchanged in the hours immediately following application of glucose shock. However, the expression of these proteins increased significantly at the end of the lag phase. Furthermore, the up-regulation of trehalose and glycogen biosynthesis proteins, first maintaining then latterly increasing glycolysis pathway activity was also observed. This was verified by enhanced ethanol yields at 10 and 12 h (0.43 and 0.45 g ethanol/g glucose) compared to 2 h (0.32 g ethanol/g glucose). These data combined with relevant metabolite measurements demonstrates that enhanced ethanol fermentation under VHG conditions can be achieved with the aid of amino acid supplementation.
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