From Cellular Function to Industrial Products
25
converted to precursor metabolites (Table 2.4) and Gibbs free energy. The Gibbs free energy is
captured in the form of high-energy phosphate bonds in ATP (anhydride-bound phosphate groups)
or as reduction equivalents typically harbored in the reduced form of two related, but distinct
compounds NADPH/NADP" and NADH/NADT.
The hydrolysis of a high-energy phosphate bond in ATP results in release of a large quantity of
Gibbs free energy:
ADP+~P-ATP-H2O = 0
;
AG° = -30.5 kJ/mole
(2.5)
where ~P is a phosphate group. The Gibbs free energy released by hydrolysis of ATP can be used
to drive biosynthetic reactions with an otherwise positive Gibbs free energy, and ATP hereby
represents a key link between the fueling reactions and the anabolism. When NAD(P)H is oxidized
to NAD(P)+
two electrons are released1, and these are transferred to other compounds inside the
cells, which consequently becomes reduced. In the following we consider the key pathways of the
catabolism.
2.1.3.1 Glycolysis
The most frequently applied energy source for cellular growth is sugars, which are converted to
metabolic products (e.g., carbon dioxide, lactic acid, acetic acid, and ethanol) with concurrent
formation of ATP, NADH, and NADPH. NADH is produced together with NADPH in the
catabolic reactions, but whereas NADPH is consumed mainly in the anabolic reactions (see Table
Table 2.4 List of precursor metabolites and some of the building blocks derived from these. The total
requirements for the precursor metabolites to synthesize
E. coli
cell mass is also specified.
Precursor metabolite
Building blocks
Amount required
IPmoles (a DW ï’l
Glucose-
6
-phosphate
UDP-glucose, UDP-galactose
205
Fructose-
6
-phosphate
UDP-iV-acetylglucosamine
71
Ribose-5-phosphate
Histidine, Tryptophane, Nucleotides
898
Erythrose-4-phosphate
Phenylalanine, Tryptophane, Tyrosine
361
Glyceraldehyde-3-phosphate
Backbone of phospholipids
129
3-Phosphoglycerate
Cysteine, Glycine, Serine, Choline,
Nucleotides
1,496
Phosphoenolpyruvate
Phenylalanine, Tryptophane, Tyrosine
519
Pyruvate
Alanine, Isoleucine, Valine
2,833
Acetyl-CoA
Lipids
3,747
2-Oxoglutarate
Arginine, Glutamate, Glutamine, Proline
1,079
Succinyl-CoA
Hemes
-
Oxaloacetate
Aspartate, Asparagine, Isoleucine,
Methionine. Threonine. Lvsine. Nucleotides
1,787
The nomenclature NAD(P)H with a parenthesis around P is used to designate either of the two co-factors.
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