1. Dr. Ng’weina Francis Magitta, MD, PhD University of Dar es Salaam 2015
GLUCONEOGENESIS
Dr. Ng’weina Francis Magitta, MD, PhD
University of Dar es Salaam
2015

2. Gluconeogenesis
The de novo synthesis of glucose and its role in preventing hypoglycemia The biosynthesis of glucose primarily from pyruvate and its precursors.

3. OVERVIEW Is not a reversal of glycolysis.
Glucose is made from non-carbohydrate precursors of carbon skeleton.
Takes place in liver, minor in kidney, brain, skeletal and heart muscle, to maintain the glucose level in the blood.
Glucose is the primary fuel of brain, and the only fuel for red blood cells.

4. Precursors for Gluconeogenesis
Gluconeogenesis begins with various substrates converted into pyruvate and this proceed though what is essentially the reverse of glycolysis (except for a few committed steps).
3 and 4-carbon substrates can enter the gluconeogenesis pathway. Lactate from anaerobic exercise in skeletal muscle is easily converted to pyruvate; this happens as part of the Cori cycle.

5. Precursors...
Oxaloacetate (an intermediate in the TCA cycle can be used for gluconeogenesis. Amino acids, after their amino group has been removed, feed into parts of the TCA, and can thus generate glucose in this pathway.
Fatty acids cannot be turned into glucose, as they are broken down into the two carbon acetyl CoA. (However glycerol which is a part of all triglycerides can be used in gluconeogenesis).

6. WHY DO WE PRODUCE GLUCOSE?
Need to maintain glucose levels within a narrow range in blood.
b) Some tissue-- brain, erythrocytes, and muscles in exertion use glucose at a rapid rate and sometimes require glucose in addition to dietary glucose.
c) The brain uses mostly glucose and erythrocytes can use only glucose as a source of energy. 6

7. GLUCUNEOGENESIS VS GLYCOLYSIS
The gluconeogenesis pathway is similar to the reverse of glycolysis but differs at critical sites.
Control of these opposing pathways is RECIPROCAL so that physiological conditions favoring one disfavor the other and vice versa.
General principles of metabolic control:
a) Pathways are not simple reversals of each other
b) Opposing pathways are under reciprocal control 7

8. KEY REACTIONS IN GLUCONEOGENESIS
PHOSPHOENOLPYRUVATE (PEP)
GDP + CO2
PEP CARBOXYKINASE
GTP
OXALOACETATE
ADP + Pi
PYRUVATE CARBOXYLASE
ATP + CO2
PYRUVATE (3C)
LACTATE, GLUCOGENIC AMINO ACIDS

9. FRUCTOSE 1, 6-BISPHOSPHATE
STEPS, CONT.
GLUCOSE Pi
GLUCOSE 6 PHOSPHATASE
GLUCOSE 6-PHOSPHATE
PHOSPHOGLUCOMUTASE
FRUCTOSE 6-PHOSPHATE Pi
F 1, 6-BISPHOSPHATASE
FRUCTOSE 1, 6-BISPHOSPHATE

10. GLUCONEOGENESIS

11. GLUCONEOGENESIS

12. GENERAL FEATURES Tissues: Subcellular location of enzymes liver (80%)
kidneys (20%)
Subcellular location of enzymes
pyruvate carboxylase: mitochondrial
glucose-6-phosphatase: ER
all other enzymes cytoplasmic

13. Malate Shuttle Oxaloacetate produced in the mitochondria matrix
Mitochondrial membrane impermeable to oxaloacetate
Malate Transporter in Mitochondrial membrane
Malate dehydrogenase in both mitochondria and cytosol
NADH produced in cytosol also used in gluconeogenesis.

14. ENERGETICS OF GLUCONEOGENESIS
Pyruvate Carboxylase
2 ATPs
PEP Carboxykinase
2 GTPs
3-P-glycerate kinase
Glyceraldehyde-3-P dehydrogenase
2NADH

15. BIOENERGETICS
Cost: The production of glucose via Gluconeogenesis is energitically expensive.
Input: 2 pyruvate + 4 ATP + 2 GTP + 2 NADH
Output: Glucose + 4 ADP + 2 GDP + 2 NAD+ + 6 Pi

16. PRECURSORS FOR GLUCONEOGENESIS
Glycerol
derived from adipocyte lipolysis
hepatic glycerol kinase

17. PRECURSORS FOR GLUCONEOGENESIS
Lactate
RBC
muscle
the Cori Cycle

18. PRECURSORS FOR GLUCONEOGENESIS
Alanine and other amino acids
transamination of pyruvate
pyruvate derived from glycolysis or from amino acid degradation
alanine cycle

19. REGULATION OF GLUCONEOGENESIS AND GLYCOLYSIS
Gluconeogenesis and Glycolysis are regulated by similar effector molecues but in the opposite direction
avoid futile cycles
PK vs PC&PEPCK
PFK-1 vs FDP’tase
GK vs G6P’tase

20. Regulation of enzyme quantity
REGULATION, CONT.
Regulation of enzyme quantity
Fasting: glucagon, cortisol
induces gluconeogenic enzymes
represses glycolytic enzymes
liver making glucose
Feeding: insulin
induces glycolytic enzymes
represses gluconeogenic enzymes
liver using glucose

21. Short-term Hormonal Effects
REGULATION, CONT.
Short-term Hormonal Effects
Glucagon, Insulin
cAMP & F2,6P2
PFK-2 & FBPase-2
A Bifunctional enzyme
cAMP
Inactivates PFK-2
Activates FBPase-2
Decreases F2,6P2
Reduces activation of PFK-1
Reduces inhibition of FBPase-1
Low blood sugar results in
High gluconeogenesis
Low glycolysis

22. Allosteric Effects REGULATION, CONT.
Pyruvate kinase vs Pyruvate carboxylase
PK - Inhibited by ATP and alanine
PC - Activated by acetyl CoA
Fasting results in gluconeogenesis
PFK-1 vs FBPase-1
FBPase-1 inhibited by AMP & F2,6P2
PFK-1 activated by AMP and & F2,6P2
Feeding results in glycolysis

23. RECIPROCAL CONTROL: GLYCOLYSIS AND GLUCONEOGENESIS ARE NOT HIGHLY ACTIVE AT THE SAME TIME
Starvation:
glucagon
rich in precursors
Fed state:
insulin 

24. The end...