Glucose metabolism

1. Glycolysis
CARBOHYDRATE METABOLISM

2. Glucose Metabolism
• Glucose occupies a central position in
metabolism in animals and microorganisms
• It is relatively rich in potential energy and so a
good fuel

3. Glucose Metabolism
• Glucose stored as starch or glycogen, provide cells
with large quantity of these hexose units for future
energy demands
• Glucose is also a remarkably versatile precursor, it
is capable of supplying a long list of metabolic
intermediates for the synthesis of other useful
macromolecules

4. The Major Pathways of Glucose Utilization

5. Carbohydrate Digestion
Other disaccharidases:
• Isomaltase
• Trehalase

6. Glucose Tissue uptake
• Reactions of intermediary metabolism take place
inside the cell (intracellularly)
• Glucose absorbed from digested dietary
carbohydrate have to be transported into the cell
in order to be available for metabolism because it
can not diffuse directly into cells

7. Glucose Transporters
• Glucose can either be transported coupled to the
movement of Na⁺ into a cell (Na⁺-
monosaccharide co-transporter system) or
• Through specialized membrane transporters
• The transporters are designated GLUT-1 to
GLUT-14. These uniporter transporter proteins
show tissue specificity

8. Glucose Transporters
• GLUT 1 is found abundantly on erythrocytes
and brain cells
• GLUT 2 is found in liver, beta cells,
hypothalamus, basolateral membrane of small
intestine and kidney (high capacity transporter)
• GLUT 3 is found in neurons, placenta and
testes

9. Glucose Transporters
• GLUT 4 is found in skeletal and cardiac
muscle and adipocytes, it’s the one activated
by insulin
• GLUT 5 found in mucosal surface in small
intestine and sperm, primarily fructose carrier
in intestine

10. Glucose Transporters
• GLUT mediate facilitated transport, from areas of
high concentration to areas of lower concentration
• Transport activity is dependent upon the sugar
concentrations and the number of transport proteins
in the outer cell membrane
• The GLUT family transports glucose both into and
out of cells

11. Glucose Transporters
• In most tissues internal glucose concentration
is lower than plasma concentration; transport
can only proceed from the extracellular space
into the cell
– Glucose phosphorylation serves to trap glucose in the cell
(extrahepatic tissues)
• In gluconeogenetic tissues (liver and kidney),
intracellular glucose can exceed blood glucose
and export of glucose occurs, usually through
GLUT2

12. Glycolysis
• Glycolysis comes from the greek words glykys,
sweet or sugar and lysis, splitting
• Its also known as Embden-Meyerhof pathway
• Occurs in the cytosol of the cell, therefore occurs
even in cells lacking organelles
– Mature erythrocytes

13. Glycolysis
• A molecule of glucose is degraded in a series of
enzyme catalyzed reactions to yield two molecules
of pyruvate, a three carbon compound
• During the sequential degradation some of the free
energy released from glucose is conserved as ATP
and NADH

14. Glycolysis
•In redox reactions, energy is released when an
electron loses potential energy as a result of the
transfer
•Electrons have more potential energy when
they are associated with less electronegative
atoms, such as C or H, and less potential energy
when they are associated with a more
electronegative atom such as O

15. Cellular Location of Glycolysis
.

19. .
Glycolysis-Investment
phase

20. Glycolysis-Payoff
hase
.

21. Reactions of Glycolysis

22. Reactions of Glycolysis

23.  Phases of
Glycolysis

24.  Glycolysis takes place in the cytosol of cells
 Glucose enters the Glycolysis pathway by conversion to
glucose-6-phosphate
 Initially there is energy input corresponding to cleavage
of two ~P bonds of ATP
H O
OH
H
OH
H
OH
CH2OPO3
2
H
OH
H
1
6
5
4
3 2
glucose-6-phosphate

25. H O
OH
H
OH
H
OH
CH2OH
H
OH
H H O
OH
H
OH
H
OH
CH2OPO3
2
H
OH
H
2
3
4
5
6
1 1
6
5
4
3 2
ATP ADP
Mg2+
glucose glucose-6-phosphate
Hexokinase
1. Hexokinase catalyzes:
Glucose + ATP  glucose-6-P + ADP
 The reaction involves nucleophilic attack of the C6
hydroxyl O of glucose on P of the terminal phosphate of
ATP
 ATP binds to the enzyme as a complex with Mg++

27.  Mg++ interacts with negatively charged phosphate oxygen
atoms, providing charge compensation and promoting a
favorable conformation of ATP at the active site of the
Hexokinase enzyme.
N
N
N
N
NH2
O
OH
OH
H
H
H
CH2
H
O
P
O
P
O
P

O
O
O

O

O O
O

adenine
ribose
ATP
adenosine triphosphate

28.  The reaction catalyzed by Hexokinase is highly
spontaneous.
 A phosphoanhydride bond of ATP (~P) is cleaved.
 The phosphate ester formed in glucose-6-phosphate has
a lower DG of hydrolysis.
H O
OH
H
OH
H
OH
CH2OH
H
OH
H H O
OH
H
OH
H
OH
CH2OPO3
2
H
OH
H
2
3
4
5
6
1 1
6
5
4
3 2
ATP ADP
Mg2+
glucose glucose-6-phosphate
Hexokinase

29. Hexokinase
• Hexokinase is inhibited by its reaction
product, G-6-P, which accumulates when
further metabolism of this hexose phosphate
is reduced. (-ve feedback inhibition)
• Hexokinase II has low Km (high affinity)
ensuring efficient phosphorylation and
further metabolism even at low glucose
concentrations in the cell.

30. Hexokinase
• Four mammalian isozymes of hexokinase have
been identified, types I – IV
– Show tissue specificity
• Type IV isozyme is glucokinase, found in
hepatocytes(liver cells)
• Glucokinase is special in the fact that it has high
Km for glucose, therefore its saturated only at very
high concentrations of glucose, not inhibited by G 6-
P

31. Hexokinase
• Glucokinase is regulated by an interplay between
fructose-6-phosphate (F6P), glucokinase regulatory
protein and insulin
• This characteristic is suited for the control of blood
sugar
• Hexokinase also phosphorylates other hexose sugars
eg galactose, fructose and mannose

32. 2. Phosphoglucose Isomerase catalyzes:
Glucose-6-P (aldose)  Fructose-6-P (ketose)
 The mechanism involves acid/base catalysis, with ring opening,
isomerization via an enediolate intermediate, and then ring
closure.
 Similar to a later reaction catalyzed by Triosephosphate
Isomerase.
H O
OH
H
OH
H
OH
CH2OPO3
2
H
OH
H
1
6
5
4
3 2
CH2OPO3
2
OH
CH2OH
H
OH H
H HO
O
6
5
4 3
2
1
glucose-6-phosphate fructose-6-phosphate
Phosphoglucose Isomerase

33. 3. Phosphofructokinase catalyzes:
fructose-6-P + ATP  fructose-1,6-bisP + ADP
 This highly spontaneous reaction has a mechanism
similar to that of Hexokinase.
 The Phosphofructokinase reaction is the rate-
limiting step of Glycolysis.
 The enzyme is highly regulated.
CH2OPO3
2
OH
CH2OH
H
OH H
H HO
O
6
5
4 3
2
1 CH2OPO3
2
OH
CH2OPO3
2
H
OH H
H HO
O
6
5
4 3
2
1
ATP ADP
Mg2+
fructose-6-phosphate fructose-1,6-bisphosphate
Phosphofructokinase

35. 4. Aldolase catalyzes:
Fructose-1,6-bisphosphate 
Dihydroxyacetone-P + Glyceraldehyde-3-P
 The reaction is an aldol cleavage, the reverse of an aldol
condensation.
6
5
4
3
2
1CH2OPO3
2
C
C
C
C
CH2OPO3
2
O
HO H
H OH
H OH
3
2
1
CH2OPO3
2
C
CH2OH
O
C
C
CH2OPO3
2
H O
H OH
+
1
2
3
fructose-1,6-
bisphosphate
Aldolase
dihydroxyacetone glyceraldehyde-3-
phosphate phosphate
Triosephosphate Isomerase

36.  A lysine residue at the active site functions in catalysis.
 The keto group of fructose-1,6-bisphosphate reacts with
the e-amino group of the active site lysine, to form a
protonated Schiff base intermediate.
 Cleavage of the bond between C3 & C4 follows.
CH2OPO3
2
C
CH
C
C
CH2OPO3
2
NH
HO
H OH
H OH
(CH2)4 Enzyme
6
5
4
3
2
1
+
Schiff base intermediate of
Aldolase reaction
H3N+
C COO
CH2
CH2
CH2
CH2
NH3
H

lysine

37. 5. Triose Phosphate Isomerase catalyzes:
dihydroxyacetone-P  glyceraldehyde-3-P
 Glycolysis continues from glyceraldehyde-3-P.
 TPI Keq favors dihydroxyacetone-P.
 Removal of glyceraldehyde-3-P by a subsequent
spontaneous reaction allows formation of GAD3P .
6
5
4
3
2
1CH2OPO3
2
C
C
C
C
CH2OPO3
2
O
HO H
H OH
H OH
3
2
1
CH2OPO3
2
C
CH2OH
O
C
C
CH2OPO3
2
H O
H OH
+
1
2
3
fructose-1,6-
bisphosphate
Aldolase
dihydroxyacetone glyceraldehyde-3-
phosphate phosphate
Triosephosphate Isomerase

38.  The ketose/aldose conversion involves acid/base
catalysis, and is thought to proceed via an enediol
intermediate, as with Phosphoglucose Isomerase.
 Active site Glu and His residues are thought to extract
and donate protons during catalysis.
C
C
CH2OPO3
2
O
C
C
CH2OPO3
2
H O
H OH
C
C
CH2OPO3
2
H OH
OH
H
H OH H+
H+
H+
H+
dihydroxyacetone enediol glyceraldehyde-
phosphate intermediate 3-phosphate
Triosephosphate Isomerase

39. TIM
Triosephosphate Isomerase
structure is an ab barrel, or
TIM barrel.
In an ab barrel there are
8 parallel b-strands surrounded
by 8 a-helices.
Short loops connect alternating
b-strands & a-helices.

40. C
C
CH2OPO3
2
H O
H OH
C
C
CH2OPO3
2
O OPO3
2
H OH
+ Pi
+ H+
NAD+
NADH 1
2
3
2
3
1
glyceraldehyde- 1,3-bisphospho-
3-phosphate glycerate
Glyceraldehyde-3-phosphate
Dehydrogenase
6. Glyceraldehyde-3-phosphate Dehydrogenase
catalyzes:
glyceraldehyde-3-P + NAD+ + Pi 
1,3-bisphosphoglycerate + NADH + H+

41. C
C
CH2OPO3
2
H O
H OH
C
C
CH2OPO3
2
O OPO3
2
H OH
+ Pi
+ H+
NAD+
NADH 1
2
3
2
3
1
glyceraldehyde- 1,3-bisphospho-
3-phosphate glycerate
Glyceraldehyde-3-phosphate
Dehydrogenase
 Exergonic oxidation of the aldehyde in glyceraldehyde-
3-phosphate, to a carboxylic acid, drives formation of an
acyl phosphate, a "high energy" bond (~P).
 This is the only step in Glycolysis in which NAD+ is
reduced to NADH.

42.  A Cysteine thiol at the active site of Glyceraldehyde-3-
phosphate Dehydrogenase has a role in catalysis.
 The aldehyde of glyceraldehyde-3-phosphate reacts with
the cysteine thiol to form a Thiohemiacetal intermediate.
H3N+
C COO
CH2
SH
H
cysteine
C
C
CH2OPO3
2
H O
H OH
1
2
3
glyceraldehyde-3-
phosphate

43.  The “high energy” acyl thioester is attacked by Pi to yield
the acyl phosphate (~P) product.
CH CH2OPO3
2
OH
Enz-Cys SH
Enz-Cys S CH CH CH2OPO3
2
OH
OH
Enz-Cys S C CH CH2OPO3
2
OH
O
HC
NAD+
NADH
Enz-Cys SH
Pi
C CH CH2OPO3
2
OH
O
O3PO
2
O
glyceraldehyde-3-
phosphate
1,3-bisphosphoglycerate
thiohemiacetal
intermediate
acyl-thioester
intermediate
Oxidation to a
carboxylic acid
(in a ~ thioester)
occurs, as NAD+
is reduced to
NADH.

44.  Recall that NAD+ accepts 2 e plus one H+ (a
hydride ion) in going to its reduced form.
N
R
H
C
NH2
O
N
R
C
NH2
O
H H
+
2e
+ H
+
NAD+
NADH

45. C
C
CH2OPO3
2
O OPO3
2
H OH
C
C
CH2OPO3
2
O O
H OH
ADP ATP
1
2
2
3 3
1
Mg2+
1,3-bisphospho- 3-phosphoglycerate
glycerate
Phosphoglycerate Kinase
7. Phosphoglycerate Kinase catalyzes:
1,3-bisphosphoglycerate + ADP 
3-phosphoglycerate + ATP
 This phosphate transfer is reversible (low DG), since
one ~P bond is cleaved and another synthesized.
 The enzyme undergoes substrate-induced
conformational change similar to that of Hexokinase.

46. C
C
CH2OH
O O
H OPO3
2
2
3
1
C
C
CH2OPO3
2
O O
H OH
2
3
1
3-phosphoglycerate 2-phosphoglycerate
Phosphoglycerate Mutase
8. Phosphoglycerate Mutase catalyzes:
3-phosphoglycerate  2-phosphoglycerate
 Phosphate is shifted from the OH on C3 to the OH on C2.

47. C
C
CH2OH
O O
H OPO3
2
2
3
1
C
C
CH2OPO3
2
O O
H OH
2
3
1
3-phosphoglycerate 2-phosphoglycerate
Phosphoglycerate Mutase
C
C
CH2OPO3
2
O O
H OPO3
2
2
3
1
2,3-bisphosphoglycerate
 An active site histidine side-
chain participates in Pi transfer,
by donating and accepting
phosphate.
 The process involves a
2,3-bisphosphate intermediate.
View an animation of the
Phosphoglycerate Mutase reaction.
H3N+
C COO
CH2
C
HN
HC NH
CH
H

histidine

48. 9. Enolase catalyzes:
2-phosphoglycerate  phosphoenolpyruvate + H2O
 This dehydration reaction is Mg++-dependent.
 2 Mg++ ions interact with oxygen atoms of the substrate
carboxyl group at the active site.
 The Mg++ ions help to stabilize the enolate anion
intermediate that forms when a Lys extracts H+ from C
#2.
C
C
CH2OH
O O
H OPO3
2
C
C
CH2OH

O O
OPO3
2
C
C
CH2
O O
OPO3
2
OH
2
3
1
2
3
1
H
2-phosphoglycerate enolate intermediate phosphoenolpyruvate
Enolase

49. 10. Pyruvate Kinase catalyzes:
Phosphoenolpyruvate + ADP  Pyruvate + ATP
C
C
CH3
O O
O
2
3
1
ADP ATP
C
C
CH2
O O
OPO3
2
2
3
1
C
C
CH2
O O
OH
2
3
1
phosphoenolpyruvate enolpyruvate pyruvate
Pyruvate Kinase

50.  This phosphate transfer from PEP to ADP is spontaneous.
 PEP has a larger DG of phosphate hydrolysis than ATP.
 Removal of Pi from PEP yields an unstable enol, which
spontaneously converts to the keto form of pyruvate.
 Required inorganic cations K+ and Mg++ bind to anionic
residues at the active site of Pyruvate Kinase.
C
C
CH3
O O
O
2
3
1
ADP ATP
C
C
CH2
O O
OPO3
2
2
3
1
C
C
CH2
O O
OH
2
3
1
phosphoenolpyruvate enolpyruvate pyruvate
Pyruvate Kinase

52. Hexokinase
Phosphofructokinase
glucose Glycolysis
ATP
ADP
glucose-6-phosphate
Phosphoglucose Isomerase
fructose-6-phosphate
ATP
ADP
fructose-1,6-bisphosphate
Aldolase
glyceraldehyde-3-phosphate + dihydroxyacetone-phosphate
Triosephosphate
Isomerase
Glycolysis continued

53. Glyceraldehyde-3-phosphate
Dehydrogenase
Phosphoglycerate Kinase
Enolase
Pyruvate Kinase
glyceraldehyde-3-phosphate
NAD+
+ Pi
NADH + H+
1,3-bisphosphoglycerate
ADP
ATP
3-phosphoglycerate
Phosphoglycerate Mutase
2-phosphoglycerate
H2O
phosphoenolpyruvate
ADP
ATP
pyruvate
Glycolysis
continued.
Recall that
there are 2
GAP per
glucose.

55. Glycolysis
Balance sheet for ~P bonds of ATP:
 How many ATP ~P bonds expended? ________
 How many ~P bonds of ATP produced? (Remember
there are two 3C fragments from glucose.) ________
 Net production of ~P bonds of ATP per glucose:
________
2
4
2

56.  Balance sheet for ~P bonds of ATP:
 2 ATP expended
 4 ATP produced (2 from each of two 3C fragments
from glucose)
 Net production of 2 ~P bonds of ATP per glucose.
Glycolysis - total pathway, omitting H+:
glucose + 2 NAD+ + 2 ADP + 2 Pi 
2 pyruvate + 2 NADH + 2 ATP
 In aerobic organisms:
 Pyruvate produced in Glycolysis is oxidized to CO2
via Krebs Cycle
 NADH produced in Glycolysis and Krebs Cycle is
reoxidized via the respiratory chain, with production of
much additional ATP.

57.  They must reoxidize NADH produced in Glycolysis
through some other reaction, because NAD+ is needed for
the Glyceraldehyde-3-phosphate Dehydrogenase reaction.
 Usually NADH is reoxidized as pyruvate is converted to
a more reduced compound, that may be excreted.
 The complete pathway, including Glycolysis and the
reoxidation of NADH, is called fermentation.
C
C
CH2OPO3
2
H O
H OH
C
C
CH2OPO3
2
O OPO3
2
H OH
+ Pi
+ H+
NAD+
NADH 1
2
3
2
3
1
glyceraldehyde- 1,3-bisphospho-
3-phosphate glycerate
Glyceraldehyde-3-phosphate
Dehydrogenase
Fermentation:
Anaerobic
organisms lack a
respiratory chain.

58. C
C
CH3
O
O
O
C
HC
CH3
O
OH
O
NADH + H+
NAD+
Lactate Dehydrogenase
pyruvate lactate
 Skeletal muscles ferment glucose to lactate during
exercise, when aerobic metabolism cannot keep up with
energy needs.
 Lactate released to the blood may be taken up by other
tissues, or by muscle after exercise, and converted via the
reversible Lactate Dehydrogenase back to pyruvate, e.g.,
for entry into Krebs Cycle.
 E.g., Lactate
Dehydrogenase
catalyzes reduction of
the keto in pyruvate to
a hydroxyl, yielding
lactate, as NADH is
oxidized to NAD+.

59. C
C
CH3
O
O
O
C
HC
CH3
O
OH
O
NADH + H+
NAD+
Lactate Dehydrogenase
pyruvate lactate
 Lactate is also a significant energy source for neurons in
the brain.
 Astrocytes, which surround and protect neurons in the
brain, ferment glucose to lactate and release it.
 Lactate taken up by adjacent neurons is converted to
pyruvate that is oxidized via Krebs Cycle.

60.  RBC,
Cornea,
Lens,
Kidney
medulla,
Testes and
Leukocyte
s
 Exercising
muscles

61. C
C
CH3
O
O
O
C
CH3
OH
C
CH3
O
H H
H
NADH + H+
NAD+
CO2
Pyruvate Alcohol
Decarboxylase Dehydrogenase
pyruvate acetaldehyde ethanol
 Some anaerobic organisms metabolize pyruvate to
ethanol, which is excreted as a waste product.
 NADH is converted to NAD+ in the reaction
catalyzed by Alcohol Dehydrogenase.

62.  Glycolysis, omitting H+:
glucose + 2 NAD+ + 2 ADP + 2 Pi 
2 pyruvate + 2 NADH + 2 ATP
 Fermentation, from glucose to lactate:
glucose + 2 ADP + 2 Pi  2 lactate + 2 ATP
 Anaerobic catabolism of glucose yields only 2 “high
energy” bonds of ATP.

63. Glycolysis Enzyme/Reaction
DGo'
kJ/mol
DG
kJ/mol
Hexokinase -20.9 -27.2
Phosphoglucose Isomerase +2.2 -1.4
Phosphofructokinase -17.2 -25.9
Aldolase +22.8 -5.9
Triosephosphate Isomerase +7.9 negative
Glyceraldehyde-3-P Dehydrogenase
& Phosphoglycerate Kinase
-16.7 -1.1
Phosphoglycerate Mutase +4.7 -0.6
Enolase -3.2 -2.4
Pyruvate Kinase -23.0 -13.9
*Values in this table from D. Voet & J. G. Voet (2004) Biochemistry, 3rd Edition, John
Wiley & Sons, New York, p. 613.

64.  Three Glycolysis enzymes catalyze spontaneous
reactions: Hexokinase, Phosphofructokinase & Pyruvate
Kinase.
 Control of these enzymes determines the rate of the
Glycolysis pathway.
 Local control involves dependence of enzyme-
catalyzed reactions on concentrations of pathway
substrates or intermediates within a cell.
 Global control involves hormone-activated production
of second messengers that regulate cellular reactions for
the benefit of the organism as a whole.
 Local control of Hexokinase and Phosphofructokinase
will be discussed here. Regulation by hormone-activated
cAMP signal cascade will be discussed later.

66.  Hexokinase is inhibited by its product glucose-6-
phosphate.
 Glucose-6-phosphate inhibits by competition at the
active site, as well as by allosteric interactions at a
separate site on the enzyme.
H O
OH
H
OH
H
OH
CH2OH
H
OH
H H O
OH
H
OH
H
OH
CH2OPO3
2
H
OH
H
2
3
4
5
6
1 1
6
5
4
3 2
ATP ADP
Mg2+
glucose glucose-6-phosphate
Hexokinase

67.  Cells trap glucose by phosphorylating it, preventing exit
by glucose carriers.
 Product inhibition of Hexokinase ensures that cells will
not continue to accumulate glucose from the blood, if
[glucose-6-phosphate] within the cell is ample.
H O
OH
H
OH
H
OH
CH2OH
H
OH
H H O
OH
H
OH
H
OH
CH2OPO3
2
H
OH
H
2
3
4
5
6
1 1
6
5
4
3 2
ATP ADP
Mg2+
glucose glucose-6-phosphate
Hexokinase

68.  Glucokinase, a variant of Hexokinase found in liver,
has a large KM for glucose. It is active only at high
[glucose].
 Glucokinase is not subject to product inhibition by
glucose-6-phosphate.
 Liver will take up & phosphorylate glucose even when
liver [glucose-6-phosphate] is high.
 Liver Glucokinase is subject to inhibition by
glucokinase regulatory protein (GKRP).

70.  Glucokinase, with its large KM for glucose, allows the
liver to store glucose as glycogen, in the fed state when
blood [glucose] is high.
Glycogen Glucose
Hexokinase or Glucokinase
Glucose-6-Pase
Glucose-1-P Glucose-6-P Glucose + Pi
Glycolysis
Pathway
Pyruvate
Glucose metabolism in liver.

71.  Glucose-6-phosphatase catalyzes hydrolytic release of
Pi from glucose-6-P. Thus glucose is released from the
liver to the blood as needed to maintain blood [glucose].
 The enzymes Glucokinase & Glucose-6-phosphatase,
both found in liver but not in most other body cells,
allow the liver to control blood [glucose].
Glycogen Glucose
Hexokinase or Glucokinase
Glucose-6-Pase
Glucose-1-P Glucose-6-P Glucose + Pi
Glycolysis
Pathway
Pyruvate
Glucose metabolism in liver.

72.  Phosphofructokinase is usually the rate-limiting step of
the Glycolysis pathway.
 Phosphofructokinase is allosterically inhibited by ATP.
 At low concentration, the substrate ATP binds only at
the active site.
 At high concentration, ATP binds also at a low-affinity
regulatory site, promoting the tense conformation.
CH2OPO3
2
OH
CH2OH
H
OH H
H HO
O
6
5
4 3
2
1 CH2OPO3
2
OH
CH2OPO3
2
H
OH H
H HO
O
6
5
4 3
2
1
ATP ADP
Mg2+
fructose-6-phosphate fructose-1,6-bisphosphate
Phosphofructokinase

73.  The tense conformation of PFK, at high [ATP], has lower
affinity for the other substrate, fructose-6-P. Sigmoidal
dependence of reaction rate on [fructose-6-P] is seen.
 AMP, present at significant levels only when there is
extensive ATP hydrolysis, antagonizes effects of high ATP.
0
10
20
30
40
50
60
0 0.5 1 1.5 2
[Fructose-6-phosphate] mM
PFK
Activity
high [ATP]
low [ATP]

75.  Inhibition of the Glycolysis enzyme Phosphofructokinase
when [ATP] is high prevents breakdown of glucose in a
pathway whose main role is to make ATP.
 It is more useful to the cell to store glucose as glycogen
when ATP is plentiful.
Glycogen Glucose
Hexokinase or Glucokinase
Glucose-6-Pase
Glucose-1-P Glucose-6-P Glucose + Pi
Glycolysis
Pathway
Pyruvate
Glucose metabolism in liver.

79.  Covalent
Modification of
Pyruvate Kinase
results in
inactivation of
enzyme.

80. Effect of
Glucose
concentration
on the rate of
phosphorylatio
n catalyzed by
Hexokinase and
Glucokinase

82. Effect of Insulin and
Glucagon on the
Synthesis of the key
Enzymes of
Glycolysis in the
liver.

90.  Alternative fates of
Pyruvate