Download Pentose Phosphate Pathway

GLYCOLYSIS AND ALTERNATIVES
BIOT 309
Fall 2013
GLYCOLYSIS AND ALTERNATIVES
• Bacteria use 3 different pathways to convert
glucose to PGA (3-phosphoglycerate) (see diagram)
1. Embden-Myerhoff (shown in next slide)
2. Entner-Dordoroff (ED) Pathway
3. Pentose Phosphate Pathway (shunt)/hexose
monophosphate shunt
Energy yields are different.
What are they?
QUICK
REVIEW
EMP
GLYCOLYSIS
ENTNER-DUODOROFF PATHWAY
• Uses EMP pathway for some steps
• Unique enzymes and intermediates
ED PATHWAY*
* Be aware that this figure does not show ATP use
or production since enzymes from EMP pathway
perform these reactions.
ED PATHWAY
• Glucose begins pathway
• E yield = 1 ATP + 1 NADH + 1 NADPH
• * From G6P to KDG split enzymes
are
different
• Pyruvate formation
• Directly 
• Indirectly – G3P enters EMP < - -
*
*
<---
*
*

*
Entner
Duodoroff
Pathway
What do
abbreviations
stand for?
MAKE a list!!!
SIDE-BY-SIDE
COMPARISON
From G6P
to
KDG/KDPA
split into
G3P +
pyruvate
enzymes
different
THIRD GLYCOLYSIS PATHWAY
Pentose Phosphate Pathway (PPP) =
Hexose Monophosphate Pathway (HMP) =
Phosphogluconate Pathway
Sometimes called a shunt.
• Operates at same time as EMP
It’s a shunt
PPP is a shunt
• The pathway begins with the glycolytic
intermediate glucose 6-P.
• It reconnects with glycolysis because two of
the end products of the PPP are
glyceraldehyde 3-P and fructose 6-P; two
intermediates further down in the glycolytic
pathway.
• It is for this reason that the PPP is often
referred to as a shunt.
PPP
• Provides ribose-5-phosphate = precursor to ribose
and deoxyribose in nucleic acids
• Provides erythrose phosphate = precursor for
synthesis of aromatic amino acids
• Other intermediates used in other pathways
• Provides NADPH – major source of energy for
anabolic reactions, e.g., nucleic acids, lipids
• Used exclusively by Thiobacillus novellus and Brucella
abortus
PATHWAY INTERMEDIATE USES
1st Reaction
High [NADPH]
inhibits
allosterically
irreversible
High [NADP+]
stimulates
allosterically
irreversible
MAKES SUGARS WITH DIFFERENT CARBON NUMBERS
All reversible
2 enzymes convert
ribuloe-5-Pi to a
ketose and an aldose
both with 5 C
Transketolase 1
2 5C 1 7C + 1 3C
Transketolase 2
1 7C +1 3C  4C+6C
Transketolase 3
4C+5C  6C + 3C
Transketolase
• Requires thiamine diphosphate (TDP) and
Mn2+ as co-factors
• TDP (TPP) is needed for redox
Regulation
• G-6-P is partitioned between EMP and PPP
• Depends on
– NADP+ and NADPH concentrations
• NADP+ high favors EMP
• NADPH high favors PPP
ENTNER-DUDOROFF PATHWAY
• The Entner-Doudoroff pathway yields one ATP
and two NADPH molecules from one glucose
molecule.
• Uses 4 enzymes that are different from EMP
1 Glucose
2 pyruvate + 1 ATP + 1 NADH
+ 1 NADPH
Bacteria: Pseudomonas, Rhizobium,
Azotobacter, Agrobacterium, Enterococcus
faecalis
PENTOSE PHOSPHATE SHUNT
PATHWAY
•
•
•
Precursors to the ribose and deoxyribose in nucleic acids
Provides erythrose phosphate which is a precursor for synthesis of aromatic
amino acids
reducing power = NADPH
Overall Oxidative Reaction: 1 Glucose 6 – P + 2 NADP+ + 1 H2O 
1 Ribose 5-P + 1 CO2+ 2 NADPH + 2 H+
Non-Oxidative Reactions
• change number of carbons in sugar molecules
• make intermediates used in other biosynthetic pathways including
feeding back into PPP and EMP
Used exclusively by Thiobacillus novellus and Brucella abortus
Additional Topics
Coenzyme A
• CoASH
• Free SH
• role in TCA
alpha KG -> succinyl CoA
Coenzyme A
• = acyl group carrier, donates acyl group to
other molecules
– Acetyl = acetyl CoA
– Succinyl = succinyl CoA
• Roles in
– Oxidation of pyruvate in TCA
– Synthesis and oxidation of fatty acids
Acetyl Coenzyme A Structure
*
*
What is this?
Vitamin B5
END