4
Gluconeogenesis
1
Blood Lecture glucose level is critical
Lehninger, Fig. 23-11
2
Important concepts
1. Non-carbohydrate precursors, where to enter the
pathway
Cori cycle
2. All metabolites and enzymes (difference with
glycolysis)
Biotin
Malate shuttle
Small molecule structure (<6 carbon)
Balance sheet for ATP and NADH
3. Regulatory steps and mechanisms
3
Gluconeogenesis
Cori Cycle
Covert pyruvate to glucose
Mostly in liver, some in kidney
Non-carbohydrate precursors
Lactate
Most amino acids, except Leu
and Lys
Glycerol
! Not fatty acids in animals
In animal, no conversion from
Acetyl-CoA to oxaloacetate
4
Lactate converted to pyruvate
5
Glycerol converted to DHAP
6
Glycolysis: How do you go backwards?
Hexokinase
GAPDH
PG kinase
PGI
Principle: Breakdown
and synthesis have key steps
that are different
PG mutase
PFK
Enolase
Aldolase
Pyruvate Kinase
TIM
7
Note difference between G and G
Reactions of glycolysis
Why the difference? 8
-22
Pyruvate set to 0 9
Glycolysis vs.
gluconeogenesis
cytosal
mitochondrion
10
Important concepts
1. Non-carbohydrate precursors, where to enter the
pathway
Cori cycle
2. All metabolites and enzymes (difference with
glycolysis)
Biotin
Malate shuttle
Small molecule structure (<6 carbon)
Balance sheet for ATP and NADH
3. Regulatory steps and mechanisms
11
Pyruvate to Oxaloacetate
Citric Acid Cycle
Intermediate
Pyruvate carboxylase uses ATP to add carboxyl
(using HCO3-)
biotin cofactor
Activated by Acetyl-CoA
12
Pyruvate carboxylase
Biotin is a covalently attached prosthetic group (through Lys)
Biotin a CO2 carrier
The activated CO2 is transferred to pyruvate
13
Pyruvate to PEP: PEP carboxykinase
But then carboxyl immediately removed
exergonic decarboxylation
Phosphoenolpyruvate (PEP) carboxykinase uses
GTP
nucleoside diphosphate kinase
ATP = GTP = UTP = CTP = TTP
Problem of compartmentalization First step in
14
mitochondrion, others in cytosol (aspartate-malate shuttle)
Glycolysis vs.
gluconeogenesis
cytosal
mitochondrion
15
Compartment
Processes
Cytosol
Glycolysis
Pentose Phosphate Pathway
Fatty Acid Biosynthesis
Many of gluconeogenesis
oxaloacetate
Mitochondrion
Citric Acid Cycle
Oxidative Phosphorylation
Fatty Acid Oxidation
Amino Acid Breakdown
Smooth endoplasmic
reticulum
Lipid biosynthesis
16
Malate shuttle
transports
oxaloacetate to
cytoplasm
17
Oxaloacetate ~ Malate ~ Aspartate
a
a
a
Malate
Oxaloacetate is a-keto acid of Aspartate (a -amino acid)
Malate is a-alcohol of Aspartate
18
Pyruvate ~ Lactate ~ Alanine
a
a
a
OH
Lactate
Pyruvate is a-keto acid of Alanine (a -amino acid)
Lactate is a-alcohol of Alanine
19
Why carboxylate and glycolysis:
Reverse de-carboxylate?
In reaction is
highly endergonic
In gluconeogenesis:
G0= +0.8 kJ/mol
Decarboxylation often drive endergonic reactions
20
Pyruvate to PEP: Pyruvate carboxylase
Pyruvate carboxylase and PEP carboxykinase 1 ATP
and 1 GTP
Remember 2 pyruvates needed per 1 glucose, so 2 ATP
21
and 2 GTP per glucose
-22
Pyruvate set to 0 2
2
Reverse steps to F-1,6-P
Where does the
NADH come
from?
Use 2 NADH/glucose
Another 2 ATP/glucose
23
Malate Shuttle
also moves
NADH into
cytoplasm
24
-22
Pyruvate set to 0 5
2
Glycolysis: How do you go backwards?
Hexokinase
PGI
PFK
GAPDH
PG kinase
PG mutase
Enolase
Aldolase
Pyruvate Kinase
TIM
26
Fructose bis-phosphatase
Opposite of regulatory
enzyme
phosphofructokinase
(PFK)
Phosphatases carry
out the opposite
reactions of kinases
27
-22
Pyruvate set to 0 8
2
Glucose-6-phosphatase
Phosphoglucose Isomerase (PGI)
Glucose-6-phosphatase is regulated and present only in
liver and kidney, to maintain glucose concentration in the
bloodstream
29
Opposite of hexokinase
G6P->glucose in endoplasmic reticulum
Glucose 6-phosphatase is stablized by an Ca2+
binding protein-SP
30
Glucose-6-phosphatase
Review
Fructose bisphosphatase
Pyruvate carboxylase
PEP carboxykinase
-22
Pyruvate set to 0 1
3
Gluconeogenesis vs. Glycolysis
Gluconeogenesis
costs 2 NADH
and 6 ATP
2 NADH
equivalent
Glycolysis
yields 2 NADH
and 2 ATP
2
2
2
32
Important concepts
1. Non-carbohydrate precursors, where to enter the
pathway
Cori cycle
2. All metabolites and enzymes (difference with
glycolysis)
Biotin
Malate shuttle
Small molecule structure (<6 carbon)
Balance sheet for ATP and NADH
3. Regulatory steps and mechanisms
33
Glycolysis and Gluconeogenesis reciprocal
regulation in liver
Energy needed:
glycolysis
Energy surplus:
gluconeogenesis
Citrate and acetyl-CoA
indicate the activity of
citric acid cycle
Allosteric control 3434
Glycolysis and Gluconeogenesis balanced in
the liver, sensitive to blood-glucose
concentration (hormone control)
Insulin and glucagon also regulate
transcription of enzymes
phosphofructokinase 2 (PFK2) catalyzes F-2,6-BP formation35
fructose bisphosphatase 2 (FBPase2) dephosphorylates F-2,6-BP
A bifunctional enzyme of PFK2+FBPase2
PFK2
FBPase2
36
Substrate cycle amplifies metabolic signals
20% increase
20% decrease
380% net flux increase
37
Integrated regulation
38
Important concepts
1. Non-carbohydrate precursors, where to enter the
pathway
Cori cycle
2. All metabolites and enzymes (difference with
glycolysis)
Biotin
Malate shuttle
Small molecule structure (<6 carbon)
Balance sheet for ATP and NADH
3. Regulatory steps and mechanisms
39