glycolysis chapter 16 – voet and voet 2 nd edition wed. september 25, 2002 1. the glycolytic...
TRANSCRIPT
GlycolysisChapter 16 – Voet and Voet 2nd Edition
Wed. September 25, 2002
1. The Glycolytic Pathway
2. The Reactions of Glycolysis
3. Fermentation: The Anaerobic Fate of Pyruvate
4. The Glycolytic Flux
5. Metabolism of Hexoses Other Than Glucose
GlycolysisGlucose is convertedto pyruvate whilegenerating two ATPs.2 molecules of NAD+
are converted to 2 molecules of NADH.
The oxidizing power of NAD+ must be recycled.
Pathway Overview
• There are 10 enzyme-catalyzed reactions considered to occur in two stages– Stage I (reactions 1-5): Preparatory stage where
glucose is phosphorylated and cleaved to yield 2 molecules of glyceraldehyde-3-phosphate (GAP). Stage I uses 2 ATPs.
– Stage II (reactions 6-10) Payoff stage where 2 GAPs converted to pyruvate and generation of 4 ATPs.
2. The Reactions of GlycolysisStage I (Preparatory Stage)
1. Hexokinase (first ATP utilization)
2. Phosphoglucose Isomerase (PGI)
3. Phosphofructokinase -1 (PFK-1) (second ATP utilization)
4. Aldolase
5. Triose Phosphate Isomerase (TIM)
Phosphoglucose Isomerasecatalyzes the conversion ofG6P to F6P, the isomerizationof an aldose to a ketose.
Step 2 – Phosphoglucose Isomerase (PGI)
[Phosphohexose isomerase]
D. Step 4 - Aldolase
• Aldolase catalyzes cleavage of fructose-1,6-bisphosphate (FBP) in reaction 4 of glycolysis.
• This forms two trioses– Glyceraldehyde-3-phosphate (GAP)– Dihydroxyacetone phosphate (DHAP).
Step 4 - Aldolase. Aldol cleavage of FBP to form twoTrioses (GAP and DHAP)
Note that the atomnumbering system changes. Atoms 1, 2, and 3 of glucose becomeatoms 3,2, and 1 ofDHAP. Atoms 4, 5, and6 become atoms 1, 2, and 3 of GAP.
Stage II - payoff phase
• 6. Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) first "High-energy" intermediate formation.
• 7. Phosphoglycerate Kinase (PGK): First ATP Generation.
• 8. Phosphoglycerate Mutase (PGM).• 9. Enolase: second "High-energy" intermediate
formation.• 10. Pyruvate Kinase (PK): Second ATP generation.
(F) Step 6 - Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH): First “High-Energy” Intermediate Formation.
Reaction Mechanism of PGM
(1) Catalytic amounts of 2,3-BisphosphoglycerateAre required for enzymatic activity.
(2) Incubation of the enzyme with catalytic amounts of32P-labeled 2,3-BPG yields a 32P-labeled enzyme.
Glycolysis influences oxygen transport
2,3-BPG binds to deoxyhemoglobin and alters the oxygenaffinity of hemoglobin. Erythrocytes synthesize and degrade 2,3-BPG by a detour from the glycolytic pathway.
Lower [BPG]in erythrocytesresulting fromhexokinase-deficiencyresults inincreasedhemoglobinoxygenaffinity.
[BPG]
[BPG]