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.