Biochemical Reaction Networks
185
considered from glucose:
v, :
glucose—»
biomass (CH, 80 0.5No.2) by :
-1.1 CH20 +0.1 CO2 + X + 0.1 NADH - 2.42 ATP.= 0
v2 :
glucose —* 3G
v3 :
glucose—» C 02 + 2NADH
(via
the EMP pathway and the TCA cycle)
v4:
NADH + 'A 0 2
-» P/O ATP
The rate of glucose consumption is - rs = v2 + v2
+ 1.1 v, .
Assume that no glycerol is excreted and that Tso is 0.045 mol 0 2 (C-mol glucose)1.
Determine the stoichiometry (the “black box” model) for the overall reaction based on the
assumption that rNADH
= rATP = 0, and P/O = 2. What is the lowest value of P/O for which
biomass can be produced?
c.
Assume that (the very small) 7» can be set to zero. Show that it is now possible to calculate
both 7sp and Tso based on knowledge of the P/O ratio.
(Answer:
Yso
---------------
and
YIP !
0 + 3
,
_ 6 / 7 0 + 1
sp ~
8 / 7 0 + 2
)
In this way the effect of using a more realistic value than 2 for P/O can be studied.
d.
Again assume that 7SX
= 0 and that some glycerol is excreted from the cells. Glycerol is of
course an unwanted byproduct and we wish to study the influence of YS8
on the product
yield. Show that
6 / 7 0 + 1 -(2 + 7 /7 0 )7
7sp = C-mole 3G (C-mole glucose)'1
=
8 /7 0 + 2
1 + 0.5T
7
= ----------- ^
1 2 /7 0 + 3
Calculate the reduction of 7sp compared with what is found in question c. when 7SB
= 0.05
and 0.1.
e.
Return to the stoichiometry of question b. with P/O = 2. In parallel with the glucose used to
feed this carbon-, redox- and ATP balanced set of pathways that determines production of 3
G some glucose may be used to produce biomass and C 02 by pure respiration, and for
maintenance of cells by combustion of glucose to C 02 alone. Write a carbon-, redox- and
ATP- balanced metabolic scheme for purely respiratory biomass production (overall
reaction 2), and a carbon-and redox balanced stoichiometry for the maintenance reaction
(overall reaction 3).
Show that any experimentally obtained stoichiometry containing only X, 3G and C02 can be
written as a linear combination of the three overall stoichiometries.
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