Biochemical Reaction Networks
Calculate from the answer to b the amount of HAc that should be produced when the other
rates are as stated above. Note that the result fits remarkably well with the experimentally
r ^ .
Next calculate the amounts of H2 and C 02
liberated between 10 and 15 h of
fermentation time. Check that rHLac ~ 0 to within the accuracy of the data.
Between 15 and 20 hr of fermentation time, biomass growth appears to stop [a decrease in
even indicated in Reardon
(1987), Fig. 4]. Reardon
obtained the following changes
Do these data fit the metabolic model of b? If not, give a reasonable physiological explanation
for the lack of fit of, e.g., the carbon balance. Why is no extra biomass formed?
(1987) notice a sharp increase in culture fluorescence after 15 h. They tentatively
explain this by an increase in NADH concentration in the cells. If this is true, does it point to
other flaws in the model of b after 15 h?
Papoutsakis (1984) cites some very old (1930) data from van der Lek for a typical "solvent type
fermentation" of C.
The biomass production is not stated, but for 100 moles
(18 kg) of glucose fermented the following amounts (in moles) of metabolic products are
Use the calculated expression in b for
from the expressions for rH2 and
b and check whether the model in b gives a satisfactory prediction of rH2 and rc.
In the pathway diagram two reactions used by Reardon
(1987) in their Fig. 3 have been
left out. These reactions are:
-BuCoA - 0.5 HAc + 0.5 AcCoA + HBu = 0
-AcetoAcCoA - 0.5 HAc + 0.5 AcCoA + 0.75 ac - 0.25 CO, - 0.25 ATP = 0
Reaction 14 is a parallel reaction to reaction 12, but without release of ATP. Reaction 15 is a