Biomedical Engineering Reference
In-Depth Information
EMP: Embden-Myerhof-Parnas Pathway
PP: Pentose-Phosphate Pathway
or HMP: Hexose-MonoPhosphate Pathway
Glu cose
ATP
ADP
Glucose-6-phosphate
NADP +
NADP +
NADPH
NADPH
6-phosphogluconate
Ribulose-5-phosphate
CO 2
Fructose-6-phosphate
ATP
ADP
Fructose-1,6-biphosphate
Ribose-5-phosphate
Xylulose-5-phosphate
Glyceraldehyde-3-phosphate
Sedoheptulose-3-phosphate
Dihydroxyacetone
phosphate
Glyceraldehyde-3-
phosphate
NAD +
NADH
1,3-Diphosphoglycerate
Erythrose-4-phosphate
Fructose-6-phosphate
ATP ADP
3-phosphoglycerate
2-phosphoglycerate
Phosphoenolpyruvate
ATP
ADP
Pyruvate
FIGURE 10.21 Embden-Meyerhof-Parnas (EMP) pathway and the pentose phosphate (PP) pathway. Each step
is assisted by an enzyme, which has been omitted in the figure for clearance. The scheme is without a PTS transport
system. Fructose-6-phosphate and glyceraldehyde-3-phosphate takes part in both pathways and hereby allows
recycling of carbon from the PP pathway back to the EMP pathway.
Two major pathways, the EMP pathway and the pentose phosphate (PP) pathway (see
Fig. 10.21 ), are considered as glycolysis pathways as well. For simplicity, we have neglected
to identify the enzymes involved in each step. Can you add the enzymes in the schematic?
The PP pathway is very closely resembled by the hexose monophosphate pathway (HMP).
One other important pathway that can be regarded as glycolysis is Entner-Doudoroff (ED)
pathway, which will be covered later.
In the EMP pathway, G6P is converted to pyruvate, and the overall stoichiometry from
glucose is given by
Glucose
H þ
(10.38)
One reaction (the conversion of F6P to FBP) requires a concomitant hydrolysis of ATP to
proceed, but two other reactions which run twice for every molecule of G6P produce
enough Gibbs free energy to give a net production of ATP in the pathway. Since ATP (or
PEP) is used for formation of G6P from glucose, the net yield of ATP is 2 mol per mole
of glucose converted to pyruvate. The four electrons liberated by the partial oxidation of
1 mol glucose to 2 mol pyruvate are captured by 2 mol of NAD þ leading to formation of
2 mol NADH.
The major function of the PP pathway is to supply the anabolic reactions with
reducing equivalents in the form of NADPH and to produce the precursor metabolites
ribose-5-phosphate (R5P) and erythrose-4-phosphate (E4P). Due to the branch points
NAD þ ¼ 2
þ 2
ADP
þ 2
H
PO
4 þ 2
PYR
þ 2
ATP
þ 2
H
O
þ 2
NADH
þ 2
3
2
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