1. Gluconeogenesis
Dr.S.Chakravarty MD

2. Maintenance of blood glucose during various states

3. Gluconeogenesis is the process of synthesizing glucose or glycogen from non-carbohydrate precursors.

4. Biomedical Importance
Gluconeogenesis meets the needs of the body for glucose when insufficient carbohydrate is available from the diet or glycogen reserves.
A supply of glucose is necessary especially for the nervous system and erythrocytes.
Glucose is also important in maintaining the level of intermediates of the citric acid cycle even when fatty acids are the main source of acetyl-CoA in the tissues.
Gluconeogenesis clears lactate produced by muscle and erythrocytes and glycerol produced by adipose tissue.
In ruminants, propionate is a product of rumen metabolism of carbohydrates, and is a major substrate for gluconeogenesis.
Failure of gluconeogenesis is usually fatal. Hypoglycemia causes brain dysfunction, which can lead to coma and death.

5. Tissues :- Liver and Kidney are the major gluconeogenic tissues, but the small intestine may also be a source of glucose in the fasting state.
Subcellular site :- Partly mitochondrial and partly cytosolic.

6. Substrates for Gluconeogenesis
Lactate Glucogenic amino acids Glycerol Propionate

7. Glucogenic amino acids
α-ketoglutarate Glutamate
Alanine Pyruvate
Aspartate Oxaloacetate
Alanine transaminase (ALT)
Aspartate transaminase (ALT)

8. Entry points of Glucogenic amino acids

9. Lactate NAD+ NADH + H+ Lactate Pyruvate USMLE!
Lactate Dehydrogenase (LDH)
Remember :-Conversion of Lactate to pyruvate requires NAD and not NADH

11. Glycerol ATP ADP Glycerol Glycerol 3 –P
This enzyme is absent in adipose tissue .
Glycerol kinase

12. Conversion of Glycerol to Glucose:
Triglycerides
FASTING OR LOW GLUCOSE
Glycerol
Fatty acids  Beta oxidation
Glycerol kinase
Liver
Acetyl Co-A
Glycerol 3- PO4
NAD+
Glycerol-3-po4 dehydrogenase
NADH
Dihydroxyacetone phosphate

13. Propionate – From oxidation of odd chain fatty acids

14. The pathway
Thermodynamic Barriers Prevent a Simple Reversal of Glycolysis.
Three nonequilibrium reactions in glycolysis catalyzed by hexokinase, phosphofructokinase and pyruvate kinase, prevent simple reversal of glycolysis for glucose synthesis.

15. Phosphoenolpyruvate carboxykinase
Step 1:
Pyruvate
Energy derived from fatty acid oxidation
ATP
Pyruvate carboxylase
CO2
BIOTIN
ADP
ABC carboxylase
(Mitochondria)
Oxaloacetate
GTP
GTP derived from succinate thoikinase
Phosphoenolpyruvate carboxykinase
CO2
GDP
(cytosol)
USMLE CONCEPT!!!
Phosphoenol pyruvate
Problem --Mitochondrial membrane is impermeable to OAA!!

16. Oxaloacetate formed in the mitochondria enters cytosol through Malate
NAD
NADH
Malate dehydrogenase
Malate
Mitochondria
cytosol
Malate
NADH
Malate dehydrogenase
NAD
Oxaloacetate

17. The next few steps are reversal of Glycolysis till Fructose 1,6 bisphosphate is formed.

18. Step 2: Conversion of fructose 1,6 bisphosphate to fructose 6-PO-4
Glucose
ADP, AMP
ATP
Fructose -6-PO4
(+)
(+)
PFK -1
Fructose 1,6 bisphosphatase
(+)
(-)
Fructose 1,6 Bisphosphate
Fructose 2,6 Bisphosphate
Fructose 2,6 Bisphosphate
Pyruvate
Glycolysis
Gluconeogenesis

19. Glucose-6-phosphatase
Step 3: Conversion to Glucose
Glucose
ATP
PO4
Glucokinase
Glucose-6-phosphatase
ADP
Glucose-6-po4
Glycolysis
Gluconeogenesis

20. Glucose 6-Phosphate & Glucose
& Glucose to glycogen(not shown)
Fructose 1,6-Bisphosphate & Fructose 6-Phosphate
1.Pyruvate & Phosphoenolpyruvate
GLUCONEOGENESIS

21. Regulation Glycolysis and Gluconeogenesis are regulated reciprocally.
Covalent
modification
Induction /
Repression
Allosteric

22. Induction & Repression of Key Enzymes Requires Several Hours.

23. Table 20.1
Harper 29th page 190

24. Covalent Modification by Reversible Phosphorylation Is Rapid
Glucagon and epinephrine inhibit glycolysis and stimulate gluconeogenesis in the liver by increasing the concentration of cAMP. cAMP cAMP-dependent protein kinase phosphorylation and inactivation of pyruvate kinase. They also affect the concentration of fructose 2,6-bisphosphate which is the most potent positive allosteric effector of of Phosphofructokinase -1 and inhibitor of Fructose 1,6 bisphosphatase .

25. Regulation of PFK -1 : Insulin Fructose -6-po4 PFK-2 Glucagon PFK-1
Fructose -2,6- Bisphosphate
Fructose -1,6- Bisphosphate
USMLE concept!!!
Regulation of PFK -1 :

26. Allosteric Regulation is Instantaneous !!
Glucagon (+)
Source of pyruvate ?
Pyruvate
Pyruvate Carboxylase
Pyruvate dehydrogenase
(+)
(-)
Oxaloacetate
Acetyl Co-A
Acetyl Co-A is the allosteric activator of pyruvate carboxylase
= allosteric regulation
What is the source of acetyl Co-A during starvation ?

27. Allosteric Modification Is Instantaneous
Acetyl -CoA as an is an allosteric activator of Pyruvate carboxylase. 
Phosphofructokinase (phosphofructokinase-1 )is inhibited by citrate and by normal intracellular concentrations of ATP and is activated by 5'AMP.
(5'AMP acts as an indicator of the energy status of the cell. )
When ATP is used AMP increases sensitive signal for energy state of the cell.

28. Substrate cycles allow fine tuning , rapid response & generate heat
ATP ADP A B Pi H20 NET FLUX OF B = 0 +heat
100
120
Other factors that favor AB 80
100 40
At rest the activity of PFK IS 10x greater than F1,6BPhosphatase .
During Muscle contraction , PFK activity increases and F1,6BPhosphatase falls so that rate of Glycolysis becomes 1000 fold higher than resting state.
Futile cycle may occur physiologically for generation of heat.
It takes place to a great extent in animals undergoing arousal from hibernation,
when body temp is much lower .

29. Clinical aspects
1. Pyruvate carboxylase deficiency (A.R)- 1 in 25,000 births –characterized by Hypoglycemia , lactic acidosis and Mental retardation .
2. Fructose 1,6bisphosphatase deficiency – lactic acidosis and hypoglycemia .Treatment – feed high carb. Diets and avoidance of fasting .
3. Hypoglycemia during pregnancy and in neonates – Increased risk of maternal hypoglycemia if there are long intervals b/w meals .
Premature babies are more susceptible to hypoglycemia. They have immmature non functional enzymes for gluconeogenesis and low adipose tissue mass.

30. Pyruvate carboxylase deficiency:

31. Malfunctioning of citric acid cycle – def of oxaloacetate
Malfunctioning of gluconeogenesis – def of oxaloacetate - Hypoglycemia
Malfunctioning of urea cycle – Def of Aspartate
Acetyl Co-A forms ketone bodies-KETOGENESIS

32. ALCOHOL DEHYDROGENASE
Alcohol  Acetaldehyde Acetate
Excess NADH 
EXCESS LACTATE from PYRUVATE
Excess Malate FROM OAA
Excess Glycerol 3 P from DHAP
 No or less Gluconeogenesis!!Hypoglycemia
NAD NADH NAD NADH

33. Immediately after completing a 25-mile marathon race, a healthy 24-yr old man was extremely dehydrated and thirsty. He quickly consumed a 6-pack of ice-cold beer and shortly thereafter became very weak and light-headed and nearly fainted. He complained of muscle cramping and pain. What is the most probable cause ?
Excess lactate in blood
Excess Alcohol in blood
Excess NADH
Dehydration
Electrolyte imbalance

34. Which of the following enzymes can be induced genetically by hormones in a person with prolonged history of fasting?
Glucokinase
Pyruvate Carboxylase
PFK-1
Acetyl co-A Carboxylase
Phosphofructokinase

35. In the citric acid cycle, succinate thiokinase catalyzes the cleavage of the succinyl –Co-A to succinate with formation of a high energy compound. This compound can then be used by the body in which of the following biochemical pathways?
Oxidative phosphorylation
Gluconeogenesis
Formation of creatine phosphate
Cholesterol synthesis
Fatty acid synthesis

36. Thank you