21 pentose phosphate pathways
TRANSCRIPT
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7/31/2019 21 Pentose Phosphate Pathways
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6CO2
-
ADP
ATP
Pi
PENTOSE PHOSPHATE PATHWAYS
Major functions: To provide reducing power for biosynthesis and/or for nucleotides(NADPH) RIBOSE
6 NADPH +6H+
6 NADPH +6H+
6 NADP+
6 NADP+
6 Glucose-6-P
6 6-P-gluconolactone
6 Ribulose-5-P 2 Ribose-5-P
2 Glyceraldehyde-3-P
2 Glyceraldehyde-3-P
4 Xylulose-5-P
Fructose-1,6-bis-P
5 Fructose-6-P
2 Erythrose-4-P
2 Sedoheptulose-7-P
P.OCH --C--C--C--C--CO2H H OH H
OH H OH
OHOHH OH
P -OCH -- C-- C-- C--CHO2
H H
OH OH
H H H
P-OCH -C---C---C---C---CHO2H H OH H
OH OH H OH
P P-OCH-C---C---C---CO--CH O-2 2
H H OH
OH OH H
P-OCH-C---C--2 -CO--CH OH2OH H
-OCH--C--CHO2
P-OCH-C---C---C--- --2 C CO-CH OH2OH OH OH H
H H H O
OH OH HP--OCH --C---C--- --2 C CO-CHOH2
H H OH
H
OH
OH
H OH
H
P-OCH C---C---CO---CH OH2- 2
OH OHOH
P-OCH -- C-- C-- CHO2H H
OH OH
P-OCH -C--CHO
P.OCH --C--C--C--C--COO2-
H H OH H
6 6-P-Gluconate
H2O
6 H2O
ENZYMES1.1.1.44 Phosphogluconate dehydrogenase
(decarboxylating)1.1.1.49 Glucose-6-phosphate dehydrogenase2.2.1.1 Glycolaldehydetransferase (Transketolase)2.2.1.2 Dihydroxyacetonetransferase (Transaldolase)2.7.1.11 6-Phosphofructokinase3.1.1.17 Gluconolactonase
(N.B. 2.2.1.1 Transketolase actually transfers an aldol and 2.2.1.2 Transaldolase transfers a ketol)
6 Glucose-6-P
6 Ribose-5-P
+ + 6H O
+ + 6CO22
12 NADP
12 NADPH + 12H
+
+
Glucose-6-
Ribose-5-
P
P
+
+ + CO2
2 NADP + H2O
2 NADPH + 2H
+
+
2
2
2
22
2
2
2
2
2
Nucleotides &
Nucleic Acids
6 Ribose-5-P
OXIDAT
IVE
PATHWAY
1
1
6
6
1.1.1.49
3.1.1.17
1.1.1.44
5.3.1.6
5.1.3.1
2.2.1.1
2.2.1.1
2.2.1.2
4.1.2.134.1.2.13
2.7.1.11
3.1.3.11
5.3.1.9
PATHWAY I (OXIDATIVE) PATHWAYS II and III
42
22
Inter- and intra -molecular rearrangements between3, 4, 5, 6, and 7-carbon sugars, result in the conversionof 5 hexoses into 6 pentoses - and vice versai.e. 5 Glucose-6-P 6 Ribose-5-PThis makes possible the two other Pathways (II and III) in whicheitherNADPHorRibose - but not both - are produced.
NADPH requirements include:
Fatty acid synthesis and steroid synthesis in liver cytosol
Regeneration of reduced glutathione to maintain stability of erythrocyte membranes
Reduction of ribonucleotides to deoxyribonucleotides for DNA
Cell requires BOTH NADH and RIBOSE
PATHWAY I
Reactants Products
165
5
1
1 Glucose-6-P
42
6
Designed by Donald Nicholson c 2002 IUBMB
3.1.3.11 Fructose-bisphosphatase
5.1.3.1 Ribulosephosphate epimerase5.3.1.1 Triosephosphate isomerase5.3.1.6 Ribosephosphate isomerase
5.3.1.9 Glucose-6-phosphate isomerase
4.1.2.13 Fructose-bisphosphate aldolase