Biochemical Reaction Networks
1 8 1
a.
Go through the biosynthesis pathway in
Corynebacterium glutamicum
of L-lysine from 1 mole
of pyruvate and one mole of phosphoenolpyruvate. For each step write down the chemical
formula for the intermediate and the amount of redox units harbored in the compound. Show
that the net consumption rate of C 0
2
and of 2-oxoglutarate is zero, and that 4 NADPH is
consumed while 2 NADH is produced for each mole of L-lysine produced from glucose. Prove
that this leads to a theoretical yield of % C-mole lysine (C-mole glucose)'1, and that 1/6 0 ;
must be used for each C-mole lysine produced.
b.
Can any of the NADPH requiring enzymes in the pathway from glucose to lysine possibly be
exchanged with an enzyme that uses NADH as co-factor? Or could an NADH producing
enzyme be exchanged with an NADPH producing isoenzyme? What would be the possible
thermodynamic consequences of exchanging the glutamate dehydrogenase encoded by GDH1
(using NADPH as cofactor) with the GDH2 encoded isoenzyme (using NADH to produce
glutamic acid from
2
- oxoglutarate)?
To solve this problem use the following references
1
“Biochemical Pathways” ed. G. Michal, Spektrum Verlag, Berlin, 1999
2 ’’ExPASy-Molecular Biology Server, Subsection Biological Pathways”
This reference is found at: http:// www.expasy.ch
Problem 5.4 Production of solvents (acetone and butanol) by fermentation.
Reardon
et al.
(1987) and Papoutsakis (1984) have both studied anaerobic fermentations of butyric acid
bacteria using metabolic flux analysis. We shall base our analysis of the primary metabolism of
Clostridium
acetobutylicum
on the simplified pathway scheme in Fig. 3 of Reardon
et al.
(1987), but the corresponding
pathway scheme, Fig. 1
of Papoutsakis (1984), differs only in some minor details and could also have been
used. The figure below shows the branchpoints and reactions.
BuCoA
V / / Z
\ VI2
BuOH
HBu
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