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Pentose Phosphate Pathway
Hexose monophosphate (HMP) shunt /
Phosphogluconate pathway.
• ATP is the cell’s “energy” BUT
– Cells also have….REDUCING POWER!
• Processes (such as photosynthesis)
require NADPH as well as ATP
• NADH and NADPH are NOT
interchangable
NADH and NADPH are NOT
interchangable
•
NAD+ participates in synthesis of ATP
•
•
glycoloysis, oxidative phosphorylation
NADPH is a reducing agent
•
produced in light reactions and consumed in
Calvin cycle of photosynthesis
NADP+ + 2H ---> NADPH + H+
In the cell…
[NAD+]
~ 1000
[NADH]
[NADP+]
[NADPH]
~ 0.01
3C1
3C6
2C5 to
1C7 + 1C3
3C5
1C5 to 1C5
2C5 to 2C5
1C7 + 1C3 to
1C6 + 1C4
1C4 +
1C5 to
1C6 +
1C3
B
CH2OPO32-
CH2OPO32-
H
O
O
O
C
OH
H
OH
C
OH
O
OH
O
OH
NH2
OH
O
N+
NH2
R
N
R
A
CH2OPO32-
H
O
C
OH
O
OH
OH
H
B
O
H
CH2OPO32OH
OH
C
OH
OH
OH
O
O
-O
C
O
O
A
H
H
OH
H
O
CH2OH
OH
O-
O
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
CH2OPO32-
CH2OPO32-
CH2OPO32-
3C6 ---> 3C5 + 3C1
2
3
2
Summary of carbon skeleton
rearrangements in the pentose phosphate
pathway.
3 ribulose-5-P ---> 2 xylulose-5-P + 1 ribose-5-P
CH2OH
CH2OH
O
O
O
H
OH HO
H
OH
CH2OPO3
H
H
2-
H
OH
CH2OPO32-
H
OH
H
OH
H
OH
CH2OPO32-
B
B
H
H
H
H
OH
O H
H
O
H
OH
A
A
H
OH
H
OH
H
OH
H
OH
CH2OPO32-
CH2OPO32-
H
H
O
H
OH
H
OH
H
OH
CH2OPO32-
H
H
OH
H
O
OH
H
OH
CH2OPO32-
HO
HO
H
OH
O
O-
B
H
H
OH
H
OH
CH2OPO32-
H
A
H
OH
CH2OPO32-
Transketolase: catalyzes the transfer of C2 units
R
H3C
CR
R
CH2OH
N+
HO
C
H
H
CH2OH
N
A
H
O
S
H3C
S
R
A
OH
H
O
H
OH
CH2OPO32-
H
OH
H
OH
H
OH
CH2OPO32-
H3C
H3C
C
R
C
OH
O
H
H
OH
CH2OH
N+
CH2OH
N+
S
S
R
B
CH2OPO32R
CH
X3
N
S
H
OH
H
OH
H
OH
N+
CH2OH
S
O
HO
C
R
R
CH2OH
H
CH2OPO32-
CR
H
O
HO
H
H3C
B
R
R
H
OH
O
H
H
OH
C3
CH2OPO32-
H
OH
H
OH
H
OH
CH2OPO32-
C7
Transaldolase: catalyzes the transfer of C3 units
CH2OH
HO
C7
Enzyme
+H N
3
O
H
Schiff Base Formation
H
OH
H
OH
H
OH
CH2OH
Enzyme
N+
H
CH2OPO3
HO
H
H
O
H
OH
H
OH
2-
H
B
CH2OPO32-
CH2OH
Enzyme
N+
H
HO
H
CH2OH
H
Enzyme
OH
N
H
OH
HO
H
CH2OPO32Schiff Base
Hydrolysis
CH2OH
O
HO
C6
H
H
OH
H
OH
CH2OPO32-
H
O
H
OH
H
CH2OPO32-
C3
A
H
O
H
OH
H
OH
C4
CH2OPO32-
R
H3C
CR
R
CH2OH
N+
H
O
S
HO
H3C
C
H
H
O
H
CH2OPO32-
H
OH
C5
H
OH
B
R
H3C
C
H
H
OH
CH2OH
N+
C
OH
O
S
R
CH2OPO32-
H
O
HO
H
B
H
H
OH
H
OH
CH2OPO32-
R
H3C
N+
C-
R
H3C
S
CH2OH
S
O
HO
C
R
R
CH2OH
N
H
OH
O
H
H
OH
C4
CH2OPO32-
CH2OH
S
H
OH
N+
R
A
OH
S
R
R
H3C
CH2OH
N
A
C3
CH2OPO32-
H
OH
H
OH
CH2OPO32-
C6
Summary of the pentose phosphate pathway
3G6P + 6NADP+ + 3H2O
6NADPH + 6H+ + 3CO2 + 2F6P + GAP
Important intermediates
Ribose-5-phosphate (nucleic acids, histidine)
Erythrose-4-phosphate (aromatic amino acids)
Fructose-1,6-bisphosphate + H2O --->
fructose-6-phosphate + Pi
∆G’º = -16.3 kJ/mol
Glucose-6-phosphate + H2O --->
glucose + Pi
∆G’º = -13.8 kJ/mol
A
H
O
O
P
OOH
H2C
CH2OPO32-
O
O-
H
O
OH
H
H
CH2OPO3
H
H2C
2-
O
H
B
OH
H
H
H
OH
H
H
OH
A
H
O
O
O-
P
O
H2C
H
OO
H
H
OH
H
H2C
B
OH
H
OH
OH
H
H
H
H
OH
O
H
OH
H
OH
OH
H
OH