glycogen metabolism

1. PRESENTED
BY:-
GEETANJALI
KALYAN
GOPAL ARORA
GUNEET KAUR
GUNJAN BHATIA
GURJIT KAUR

2. GLUCONEOGENESIS

3. INTRODUCTION
 It is the process by which glucose molecules are
produced from non-carbohydrate precursors.
 Gluconeogenesis meets the need of the body for
glucose when sufficient carbohydrate is not
available for from diet or glycogen reserves.
 SITE: Liver and kidney are the major two
gluconeogenic tissues.
 This process is partly mitochondrial and partly
cytoplasmic.

4. SUBSTRATES
LACTATE
GLUCOGENIC AMINO ACIDS
GLYCEROL
PROPIONYL CoA
These non carbohydrate precursors of
glucose are first converted into pyruvate
or enter pathway at later intermediates.

5. LACTATE
Lactate formed in the muscle is transported to the liver .In the
liver LACTATE DEHYDROGENASE converts lactate to pyruvate
which then enters gluconeogenic pathway.

6. GLUCOGENIC AMINO ACID
 Glucogenic amino acids include alanine, glutamic
acid, aspartic acid etc.
 When glucose is not readily available , the
glucogenic amino acids are transaminated to
corresponding carbon skeletons .These then enters
the TCA cycle to form oxaloacetate or pyruvate.
 ALANINE released from muscle is major substrate
for gluconeogenesis.

7. GLUCOSE-ALANINE CYCLE
• Alanine is transported to liver, transaminated to pyruvate and converted
to glucose .
• Glucose-alanine cycle is important in conditions of starvation

8. GLYCEROL: The glycerol part of fat is phosphorylated in the liver
Cytosol by ATP to glycerol-3-phosphate.It is then oxidized to DHAP by
NAD+ dependent dehydrogenase.
PROPIONYL CoA : It is formed from odd chain fatty acids and
carbon skeleton of some amino acids .it is converted to succinyl CoA and is a
minor source for glucose.

9. REACTIONS OF
GLUCONEOGENESIS
 IN Glycolysis, glucose is converted into
pyruvate; in gluconeogenesis, pyruvate is
converted into glucose.
 However , GLUCONEOGENESIS IS
NOT A REVERSAL OF GLYCOLYSIS.

10. HHVBB
OVERVIEW OF
GLYCOLYSIS

11. Three non equillibrium
Rxns in glycolyis catalyzed
by
• Hexokinase
• Phosphofructokinase
• Pyruvate kinase are
Considered
thermodynamic
Barriers which prevent
simple reversal of
glycolysis
for glucose synthesis

13. KEY GLUCONEOGENIC
ENZYMES
The irreversible steps in glycolysis are circumvented
by four enzymes which are designated as the key
enzymes of guconeogenesis
1. Pyruvate carboxylase
2. Phosphoenol pyruvate carboxy kinase
3. Fructose 1,6 bisphosphatase
4. Glucose-6-phosphatase

14. REACTIONS OF
GLUCONEOGENESIS
In gluconeogenesis, the following new steps
bypass these virtually irreversible reactions of
glycolysis:
1. First bypass ( Formation of phosphoenol
pyruvate from pyruvate)
2. Second bypass (Formation of fructose 6
phosphate from fructose 1,6-bisphosphate)
3. Third bypass (Formation of glucose by
hydrolysis of glucose 6 phosphate)

15. FIRST BYPASS REACTION:CONVERSION
OF PYRUVATE TO PHOSPHOENOL
PYRUVATE
 Requires participation of both mitochondrial and
cytosolic enzymes.
 Pyruvate is transported from the cytosol into
mitochondria via the mitochondrial pyruvate
transporter OR pyruvate may be generated within
mitochondria via deamination of alanine.
 Phosphoenol pyruvate is formed from pyruvate by
way of oxaloacetate through action of pyruvate
carboxylase (mitochondrial) and
phosphoenolpyruvate carboxykinase.

16. Reaction catalyzed by
pyruvate carboxylase
 Mitochondrial pyruvate carboxylase catalyzes
the carboxylation of pyruvate to OAA ,an ATP
requiring rxn in which vitamin biotin in
coenzyme.
 biotin binds CO2 from bicarbonate as
carboxybiotin prior to addition of CO2 to
pyruvate.
Pyruvate + HCO3 + ATP
Oxaloacetate +ADP + Pi +H+

17. TRANSPORTATION OF
OXALOACETATE (MALATE
ASPARTATE SHUTTLE)
 The previous reaction takes place in mitochondria
so OAA has to be transported to cytosol because
further rxns of gluconeogenesis are taking place in
cytosol .this is achieved by malate aspartate
shuttle.
 Oxaloacetate is reduced to malate by mitochondrial
malate dehydrogenase at the expense of mitochondrial
NADH.
Oxaloacetate + NADH + H+ L-malate +
NAD+

18.  Malate exits mitochondria via the
malate/αketoglutarate carrier.
 In the cytosol ,malate is reoxidized to
OAA via cytosolic malate
dehydrogenase with production of
NADH.
L-malate + NAD+ OAA
+NADH + H+

20. DECARBOXYLATION OF
OXALOACETATE
 OAA is then converted to phosphoenol pyruvate by
phosphoenol pyruvate carboxykinase in the rxn
Oxaloacetate + GTP Phosphoenol pyruvate +CO2
The overall rxn for this set of bypass is
Pyruvate+ATP+GTP+HCO3
-
PEP+ADP+GDP+Pi+H+
Thus the synthesis of PEP requires an investment of 1 ATP
and 1GTP
When either pyruvate or ATP/ADP ratio is high the rxn is
pushed towards right (biosynthesis)

21. BIOLOGICAL SIGNIFICANCE
 In the liver and kidney,the rxn of succinate
thiokinase in citric acid cycle produces GTP (rather
than ATP) and this GTP is used for rxn of
phosphoenol pyruvate carboxykinase
 Thus providing a link b/w citric acid cycle activity
and gluconeogenesis ,to prevent excessive removal
of oxaloacetate for gluconeogenesis ,which would
impair TCA cycle.

22. SECOND BYPASS :FORMATION
OF FRUCTOSE-6-PHOSPHATE FROM
FRUCTOSE-1,6-BISPHOSPHATE
 On formation PEP is metabolizes by enzymes of
glycolysis but in reverse dxn.
 Thes rxns are near equillibrium under intercellular
condiyion so when conditions favour
gluconeogenesis,the reverse rxns will take place
until next irreversible step is reached.
Fructose 1,6 bisphosphate+ H2O Fructose 6
phosphate +Pi

23. Fructose 1,6 bisphosphatasecatalyzes this exergonic
hydrolysis
 It is present in liver,kidney and skeletal muscle but
is probably absent from heart and smooth muscle.
 Like its glycolytic counterpart it is an allosteric
enzyme that particiaptes in regulation of
gluconeogenesis

24. Third bypass:FORMATION
OF GLUCOSE BY HYDROLYSIS
OF GLUCOSE 6 PHOSPHATE
 The fructose 6 phosphate generated by fructose 1,6
bisphosphatase is readily converted into glucose 6
phosphate by enzyme glucose 6 phosphatase.
 Glucose-6-phosphate + H2O glucose +Pi
 Glucose-6-phosphatase is present in the liver ,but
absent in brain and muscle.Thus,glucose produced
by gluconeogenesis in the liver,is delivered by
bloodstream to brain and muscle.

26. ENERGETICS
 The reactions catalyzed by pyruvate carboxylase , phosphoenol
pyruvate carboxykinase and phosphoglycerate kinase requires 1
ATP each ;so 3 ATPs are used by 1 pyruvate residue to produce
one half molecule of glucose;or 6 ATPs are required to generate
one glucose molecule.
 2 pyruvate2 oxaloacetate = 2 ATP
 2 oxaloacetate2 Phosphoenol pyruvate(GTP) =2 ATP
 2*3-phosphoglycerate2*1,3-bisphosphoglycerate=2 ATP
 Total=6ATP
 Whereas 2 ATP are generated in glycolytic conversion of glucose
.THUS IT IS NOT REVERSAL OF GLYCOLYSIS BUT IS
ENERGETICALLY AN EXPENSIVE AFFAIR.

28. REGULATION OF
GLUCONEOGENESIS
 Gluconeogenesis and glycolysis are coordinated so
that within a cell one pathway is relatively inactive
while other is highly active.
 The amount and activity of the distinctive enzymes
of each pathway are controlled so that both
pathways are not active at the same time.

29. GLUCONEOGENESIS AND
GLYCOLYSIS ARE
RECIPROCALLY REGULATED

30.  FIRST COORDINATED CONTROL POINT:
 Pyruvate PEP
1. Pyruvate Kinase: inhibited bt ATP and alanine .Activated by F1-
6,BP.
2. PEP Carboxylase: ADP turns it off.Thus when energy charge of
cell is low ,the biosynthetic pathway is turned off
3. Pyruvate Carboxylase: It is an allosteric enzyme.stimulated by
acetyl CoA and inhibited by ATP
Finally recall that PDH is inhibited by acetyl CoA .Thus excess acetyl
CoA shows its formation from pyruvate and stimulates
gluconeogenesis by activating pyruvate carboxylase.

31.  SECOND COORDINATED POINT:
Fructose 1,6-bisphosphateFructose6-phosphate
Thus F-1,6-Bpase is inhibited by F-2,6-BP and
AMP.
These modulators have opposite effect on PFK-1.

32.  The activities of PFK 2 and FBPase reside on same polypeptide chain
 Both activities are reciprocally regulted by phosphorylation of single serine
residue.
Thus low blood glucose, blood glucagon,  cAMP dependent
phosphorylation of this bifunctional enzyme,  PKK 2 and  FBPase 2,
which then  F2,6-BP and then PFK1 and  Fructose 1,6 bisphosphatase
Bottom line : when blood glucose is low: glycolysis decreases and
gluconeogenesis incraeses.

34. HORMONAL REGULATION OF
GLUCONEOGENESIS
 It is regulated by glucagon,insulin and glucocorticoids.
 REGULATION OF STATE OF PHOSPHORYLATION OF
HEPATIC ENZYMES
Glucagon activates adenylate cyclase to produce cAMP , which
activates protein kinase A ,which then phosphorylates and
INACTIVATES pyruvate kinase therbey decreasing glycolysis.
It stimulates gluconeogenesis by decreasing the conc of F-2,6 BP
in the liver which leads to increase in fructose 1,6-bisphosphatase
activity and thus incraesing gluconeogenesis
INSULIN CAUSES OPPOSITE EFFECT.

36. Glucagon and insulin mediate long term effects by inducing
and repressing the synthesis of key enzymes.
Glucagon induces synthesis of gluconeogenic enzymes like:
PEP-Carboxylase
Fructose 1,6-bisphosphatase
Glucose 6-phosphatase
Glucagon represses synthesis of glycolytic enzymes like;
Glucokinase
PFK 1
Pyruvate kinase
INSULIN GENERALLY OPPOSES THESE ACTIONS.

37. SIGNIFICANCE OF
GLUCONEOGENESIS
 ONLY LIVER CAN REPLENISH BLOOD SUGAR
through gluconeogenesis because glucose 6
phosphatase is present mainly in liver.So liver play
the major role in maintaining blood glucose level.
 DURING STARVATION gluconeogenesis maintain
the blood glucose level. The stored glycogen is
depleted within the first 12-18 hours of fasting .On
prolonged starvation, the gluconeogenesis is
speeded up and protein catabolism provides the
substrates namely glucogenic amino acisds.

39. GLYCOGENOLYSIS
Glycogen Phosphorylase
I. It removes glucose as glucose-1-phosphatefrom
glycogen(phosphorolysis).It contains PLP as
prosthetic group.The α-1,4- linkages in glycogen
are cleaved.
II. It removes glucose units one at a time.Enzyme
hydrolyzes alpha-1,4-glycosidic linkages,till it
reaches a glucose residue,3-4 glucose units away
from the branch point.It cannot attack the 1,6
linkages at the branch point.

40. III. If glycogen phosphorylase alone acts on glycogen
molecule,the final product is highly branched
molecule;known as limit dextrin.
Debranching by functional enzyme
I. A block of 3 glucose residues are formed from
branching point to another branch.This enzyme is
alpha-1,4alpha-1,4 glucan transferase.
II. Now the branch point is free.The alpha-1,6-
glucosidase(debranching enzyme) can hydrolyze the
remaining glucose unit held in alpha-1,6 linkage at the
branch point.

41.  III. The glucose residue is released as free glucose.At this stage,
the ratio of glucose-1-phosphate to free glucose is about 8:1.
 IV. The transferase and alpha-1,6-glucosidase will together
convert the branch point to linear one. With the removal of
brnch point phosphorylase enzyme can proceed with its
action.
 Phosphoglucomutase
 Phosphorylase reaction produces glucose-1-phosphate while
debranching enzyme releases glucose.
 Glucose-1-phosphate glucose-6-phosphate by
phosphoglucomutase.

42.  Glucose-6-phosphate in liver
Heptic glucose-6-phosphate hydrolyzes glucose-6-
phosphateto glucose. Free glucose is released to
bloodstream.
Muscle will not release glucose to blood
stream,because there is no glucose-6-phospatase in the
muscle therefore, in muscle, glucose-6phosphate
undergoes glycolysis to produce ATP for muscle
contraction.

43. GLYCOGENOLYSIS

44.  Energetics
 I. The energy yeild from one glucose residue
derived from glycogen is 3ATP is required for initial
phosphorylation of glucose.
 II. If glycolysis starts from free glucose only 2ATPs
are produced.

45. GLYCOGENESIS
 This pathway is reversal of glycogen breakdown and the steps
are:
 Activation of glucose
 Glucose-1-phosphte + UTP UDP-glucose + PPi by the
enzyme UDP-glucose phosphophorylase.
 Glycogen Synthase
 The glucose moiety from UDP- glucose is transferred to
glycogen primer(glycogenin) molecule.The primer is essential
to accept glycosyl unit .Primer is made up of protein-
carbohydrate complex.It is dimeric protein, having two
identical monomers.An oligosaccharide chain of 7 glucose
units is added to each monomer.

46.  Glycogen primer(n) + UDP-glucose 
Glycogen(n+1) + UDP-glucose
 In the next step,activated glucose units are
sequentially added by enzyme glycogen
synthase.The glucose unit is added to nonreducing
end of the glycogen primer to form an alpha-1,4
glycosidic linkage and UDP is liberated.

48.  Branching Enzyme
 I. The glycogen synthase can add glucose units only
in alpha-1,4 linkage. A branching enzyme is needed
to create alpha-1,6 linkages
 II. When the chain is lenghthened to 11-12 glucose
residues,the branching enzyme will transfer a block
of 6-8 glucose residues from the chain to another
site on growing molecule. The enzyme amylo-
[1,4][1,6]-transglucosidase (branching enzyme)
forms the alpha-1,6 linkage.

49.  III. To the newly created branch, further glucose units
can be addedin alpha-1,4 linkage by glycogen
synthase.

50. REGULATION OF
GLYCOGEN METABOLISM
 I. The synthesis and degradation pathways are
reciprocally regulated to prevent futile cycles.
 II. The phosphorylated form of glycogen
phosphorylase is active; but glycogen synthase
becomes inactive on phosphorylation. The
covalently modified phosphorylase is active even
widhout AMP. Active glycogen synthase is
responsive to the action of glucose-6-
phosphate.Covalent modification modulates the
effect of allosteric regulation are interrelated.

51. III. These hormones are through a second messenger
cyclic AMP (cAMP).
IV. The covalent modification of glycogen
phosphorylase and synthase is by cyclic AMP
mediated cascade.Specific protein kinase bring about
phosphorylation and protein phosphatase causes
dephosphorylation.

52. Regulation of glycogen synth. By cAMP
The glycogenesis is regulated by glycogen synthase.
This enzyme exists in two forms - glycogen synthase
‘a’-which is not phosphorylate and more active, and
glycogen synthase ‘b’- as phosphorylated inactive
form. So glycogen synthase a can be converted to ‘b’
form by phosphorylation.This process is catalyse by a
cAMP -dependent protein kinase .Protein kinse
phosphorylates and inactivates glycogen synthase by
converting ‘a’ form to ‘b’ form. Glycogen synthase ‘b’
can be converted back to synthase ‘a’ by phosphatase I.

53.  Regulation of glycogen degradation by cAMP
 The hormones like epinephrine and glucagon bring
about glycogenolysis by their action on glycogen
phosphorylase through cAMP.
 cAMP formed due to hormonal stimulus aactivates
cAMP dependent protein kinase. This active protein
kinase phosphorylase linase to active form. The active
phosphorylase kinase phosphorylates inactive glycogen
phosphorylase’b’ to active glycogen phosphorylase ‘a’
which degrades glycogen. The enzyme protein
phosphatase I can dephsphorlate and can convert active
glycogen phosphorylase ‘a’ to inactive ‘b’ form.

54. cAMP MEDIATED ACTIVATION
CASCADE

55. RECIPROCAL REGULATION OF GLYCOGENOLYSIS AND
GLYCOGENESIS BY cAMP

56.  Effect of calcium ions on glycogenolysis:
 When the muscle contracts, calcium ions are
released from the sarcoplasmic reticulum. Calcium
binds to calmodulin-calcium modulating protein
and directly activates phosphorylase kinase
widhout the involvement of cAMP –dependent
protein kinase.
 An elevated glucagon or epinephrine level inc.
glycogen degradation whereas an elevated insulin
results in increased glycogen synthesis.

57. Glycogen phosphorylase in liver and muscle:
A. LIVER: the liver phosphorylase-b is inactive form.It becomes
active on phosphorylation.The active enzyme is phosphorylase-
a.The enzyme is inhibited by ATP and glucose-6-phosphate.
B. MUSCLE: Skeletal muscle glycogen is only degraded when the
demand for ATP is high.The regulation of glycogenolysis in the
sk. Muscles is by epinephrine. Glucagon has no effect on muscle
glycogenolysis.AMP formed by degradation of ATPduring
muscle contraction is an a;losteric activator of phosphorylase-b.

58.  GLYCOGEN SYNTHASE
 I. Glycogen synthase and phosphorylase activities
are reciprocally regulated.
 II. The same protein kinase, which phosphorylates
the phosphorylase kinase would also phosphorylate
glycogen synthase.
 III. The activity of glycogen synthase is markedly
decreased on phosphorylation. Insulin promotes
glycogen synthesis by favouring
dephosphorylation.

59.  The reciprocal regultion of glycogenolysis and
glycogenesis is by covalent modification .Insulin
and glucagon are major regulatory hormones
,although epinephrine has stimulatory effect on
glycogenolysis in both liver and miuscle.THey bring
about alteration in activity of protein kinase and
phosphatases by varying the level of cAMP.

60. GLYCOGEN STORAGE
DISEASES
 The metabolic defects concerned with the glycogen synthesis and
degradation are collectively referred to as Glycogen storage diseases.
 These are due to deposition of normal or abnormal type of glycogen in
one or more tissues.
1) Von Gierke’s disease/ Glycogen storage disease type 1 - In this
disease, glucose 6 phosphatase is deficient.
2) The characteristic features are :-
 Fasting hypoglycemia – due to defect in glucose 6 phosphatase, free
glucose is not released from the liver.
 Lactic acidemia – glucose is not synthesized from lactate produced in
muscle and liver. Due to it, lactate level in blood increases and ph is
lowered.

61.  Hyperlipidemia – there is blockage in
gluconeogenesis. Therefore more fat is mobilized to
meet energy requirements of the body. It results in
increased plasma free fatty acids and ketone bodies
which lead to ketosis.
 Hyperuricemia – Glucose 6 phosphate which
accumulates is diverted to HMP pathway, leading to
increased synthesis of ribose phosphates. It will
increase the phosphoribosyl pyrophosphate and
enhance the metabolism of purine nucleotides to uric
acid. Elevated plasma levels of uric acid will lead to
gouty arthritis.
 Glycogen gets deposited in the liver. Massive liver
enlargement may lead to cirrhosis.
 Children usually die in early childhood.

62. 2) Pompe’s disease – It occurs due to deficiency of enzyme
Lysosomal alpha-1,4 glucosidase. Glycogen accumulates in
lysosomes in almost all the tissues. Heart is mostly involved
organ. Enlarged liver and nervous system is also affected.
Adults die from muscular dystrophy and death occurs in
early stage due to heart failure.
3) Cori’s disease – It occurs due to debranching enzyme Amylo
alpha-1,6 glucosidase. Clinical features include liver
enlargement, fasting hypoglycemia, hepatomegaly, and
myopathy. Enzyme replacement therapy is nowadays
available for the treatment of infantile-onset Pompe’s disease.
4)Anderson’s disease – It is rare disease and occurs due to
deficiency of branching enzyme Glucosyl4-6 transferase. It
occurs in almost all tissues of our body. Clinical features are
cirrhosis of liver, impairment in liver function and death
occurs before the age of 5 yrs.

63. 5) McArdle’s disease – Muscle phosphorylase enzyme is
deficient in the disease. It commonly occurs in skeletal
muscle . Clinical features are exercise intolerance ,
accumulation of glycogen in muscles, and
myoglobinurea.
6) Her’s disease – It occurs due to deficiency of enzyme
liver phosphorylase. It mostly occurs in liver. Clinical
features are mild hypoglycemia, hepatomegaly,
hyperlipidemia, and ketosis.
7) Tauri’s disease – Phosphofructokinase enzyme is
deficient in this disease. It occurs in both skeletal muscle
as well as erythrocytes. Subject will complain about
muscle cramps during exercise. Glycogen will
accumulate in muscles and hemolytic anaemia will also
be seen as an important feature.

64. 8) Type VIII disease – it occurs due to deficiency of liver
phosphorylase kinase. Mild hypoglycemia can be seen in
the patients who suffer from this disease.
9) Type IX a , b – Muscle phosphorylase kinase enzyme is
deficient in this disease. Clinical features of this disease
are the same as Her’s disease.

65. HEXOSE
MONOPHOSPHATE
(HMP) SHUNT
PATHWAY