3.3. Identification of regulators for the selected reactions
In this section, new compounds have been added to the medium, not only as a nutrient but also as a regulator to maintain the flux distributions at the optimum pH level. To assess the model’s power to detect unknown yeast bottleneck reactions, we have used the Brenda database to identify activators/inhibitors for the target reactions (Table S8). The available BRENDA activators and inhibitors have been applied separately to the medium for the assessment of each efficient regulator. The concentrations (extracted from BRENDA) and the effects of each regulator on ethanol yield are shown in Figure 6 and providing information on glucose depletion time and yeast growth were presented in Table S3, 8. In order to precisely evaluate the regulatory effect of each compound, ethanol yield production was assessed as moles of produced ethanol per one carbon mole of all added carbon sources in the medium. The control sample yield (without any regulator) was 0.18 mole ethanol/mole carbon equals to 5.5 g/l ethanol. We experimentally tested 15 regulators and 11 compounds were selected for more evaluation, including EDTA, glycerol, sodium acetate trihydrate, and cysteine as the activator and glycine, ammonium chloride, imidazole, zinc chloride, calcium carbonate, magnesium sulfate, and zinc sulfate as the inhibitor. The other four remaining compounds (including copper (II) chloride, copper (II)chloride dehydrate, phenanthroline monohydrate, silver nitrate) were inhibited growth and were excluded from optimization experiments.