Russian National Research Medical University
The sweet side of catabolism:
carbohydrates as cellular fuels
Maxim A. Abakumov
Moscow, 2014
Carbohydrates metabolism
• Usually comes as polysaccharides
• Two main polysacharides are glicogen and
starch
• Polysacharides can not be used in native form
• Breakdown into monosacharides and transport
from gut to blood stream and periheral tissues
are needed
Digestion of carbohydrates
• Digestion – enzyme driven breakdown of large
polysacharide molecules into monosacharides
• Usually takes plase in gastrointestinal tract
Glucose polymers
Starch, glycogen
Disaccharides
Digestion by
amylase
Maltose
Maltase
Sucrose
Sucrase
Lactose
Lactase
Monosaccharides
2xGlucose
Glucose+Fructose
Glucose+Galactose
Absorption of carbohydrates
• Process of monosacharides transport from gut to blood stream or lymph
• Involves special transporting proteins located on membrane of intestine cells
Digestion
Composition of carbohydrates in your
diet:
~ 70% starch (polysaccharide)
~ 20% sucrose (disaccharide)
~ 6% lactose (disaccharide)
~ 2% maltose (disaccharide)
• Polysacharides digestion occurs in mouth and small
intestine
• This process is driven by salivary and pancreatic
amylases
Digestion
Absorption
• Transmembrane transporter proteins are
involved
• First, monosacharides are transported into cell
from intestine
• Second, monosacharides are released into
blood stream
Absorption
Glucose metabolism
• Glucose decomposition for energy release (ATP
synthesis) called glycolysis
• Glucose synthesis with energy consume (ATP
hydrolysis) calles gluconeogenesis
• Glycolysis can be diveded into:
a) aerobic
b) anaerobic
• Aerobic products are CO2 and H2O
• Anaerobic product is lactate
• For both intermediate is pyruvate
Glucose metabolism in cell
Glucose
Anaerobic Glycolisis
Lactate
Pyruvate
AcetylCoa
TCA
TCA
ETC+OP
CO2 + H2O + ATP
Aerobic Glycolisis
Glycolisis
Glucose
Glucose-6-P
Fructose-1,6-diP
Fructose-6-P
O
O
-
O
-
O P O
HO
O H
H
H
OH
O H
H
OH
HO
OH
OH
ATP
H
PO3H2
O
8
H2PO4
O
ATP
ATP
CH2
H2PO4
7
CH3
O
O
Phosphoenol
pyruvate
O
10
ATP
HO
Pyruvate
O
H2PO4
-
HO
OH
H
ADP
OH
H
4
5
NAD+
NADH
PO3H2
6
1. Glucokinase
2. Phosphogluco
isomerase
3. Phosphofructo
kinase-1
4. Aldolase
5. Triosophosphate
isomerase
PO3H2
O
O
HO
HO
HO
ADP
PO3H2
O
O
H2O
ADP
H
1,3-bisphospho
glycerate
HO
HO
H
O P O
O
OH
OH
-
O
HO
H
3-phospho
glycerate
HO
O
-
O
3
OH
OH
O
O P O
-
O
OH
H
ADP
2
H
HO
2-phospho
glycerate
9
O P O
H
H
H
-
O
1
-
O
HO
O
OH
6. Glyceraldehyde phosphate
isomerase
7. Phosphoglycerate kinase
8. Phosphoglycerate mutase
9. Enolase
10. Pyruvate kinase
Glucose metabolism in cell
Sequence of reactions
Glucose
+
Pyruvate
Aerobic Glycolisis
2x
Anaerobic Glycolisis
CoA + CO2
TCA, ETC, OP
Lactate
Glucose phosphorylation
• First step in glucose metabolism – phoshorylation
of OH-group at 6th carbon atom
• Phosporylated glucose (glucose-6-phospate) is
charged and cannot be transported out of the cell
• Glucose-6-P goes to metabolism
• Catalyzed by two types of enzyme (isozymes)
Glucose phosphorylation
Hexokinase
• Low Km value
Glucokinase
• High Km value
• High affinity to glucose
• Low affinity to glucose
• Located in most tissue cells
• Located mostly in liver cells
• Three isoforms (I, II, III)
•Actually IV isoform of hexokinase
18
Glucose-2- F
• PET tracer
• Indicates glucose cosumption by cells
• Phosphorylates after transport in cell
• OH-group at 2nd carbon atom is substituted by 18F
• Further metabolism is blocked
• Cells with more active metabolism increase glucose
consumption, glucose-2-18F level and consequently
signal on PET scanner
Phase I
• Coversion of glucose (6 carbon) to
dihydroaceton phosphate and gliceraldehyde-
3-phosphate (2x3 carbon)
• 2 ATP are required (will be regenerated later)
• 1st and 3rd reaction are irreversible
Phase I. Preparatory phase.
Glucose
Glucose-6-P
Fructose-1,6-diP
Fructose-6-P
O
O
-
O
-
O P O
HO
H
OH
H
OH
OH
H
OH
O H
H
H
HO
ATP
O P O
O
1
O H
H
-
ADP
OH
OH
2
O
O P O
-
O
OH
O
H
H
HO
H
-
3
-
H
O
HO
OH
H
ATP
-
O
H
OH
OH
O P O
O
HO
H
-
ADP
OH
H
4
1. Glucokinase
2. Phosphogluco
isomerase
3. Phosphofructo
kinase-1
4. Aldolase
5. Triosophosphate
isomerase
PO3H2
PO3H2
O
O
HO
O
D-glyceraldehyde
-3-phosphate
5
O
OH
Dyhydroxy
acetone
phosphate
Glucose to glucose-6-P
1st ATP is hydrolysed
Total ATP count: -1 ATP
Total NADH count: 0 NADH
O
Glucose-6-P to fructose-6-P
O
P
O
O
O
O
O H
H
H
OH
P
O
O
H
H
OH
H
H
OH
OH
CH2OH
O
Phosphohexose
isomerase
Total ATP count: -1 ATP
Total NADH count: 0 NADH
OH
OH
OH
H
Fructose-6-P to fructose-1,6-diP
OH
O
ATP
P
H2C
O
HO
H
O
P
OH
P
O
H
HO
OH
OH
O
HO
HO
H
ADP
Phosphofructokinase-1
OH
HO
OH
H
H
OH
H
Fructose-1,6-diP
Fructose-6-P
2nd ATP is hydrolysed
Total ATP count: -2 ATP
Total NADH count: 0 NADH
OH
Fructose-2,6-diP to gliceraldehyde-3phosphate and dihidroxyacetone-phosphate
OH
O
O
P
OH
P
O
HO
H
OH
Fructose-2,6-diP
HO
OH
H
OH
H
Aldolase
PO3H2
PO3H2
O
O
HO
O
O
OH
Dyhydroxyacetone
phosphate
Total ATP count: -2 ATP
Total NADH count: 0 NADH
D-glyceraldehyde3-phosphate
Phase II. Payoff phase
• Coversion of dihydroaceton phosphate and
gliceraldehyde-3-phosphate (2x3 carbon) to
pyruvate (2x3 carbon)
• 4 ATP are restored
• Last reaction is irreversible
Phase II. Payoff phase.
2-phospho
glycerate
3-phospho
glycerate
ATP
PO3H2
HO
H2PO4
O
ADP
O
8
PO3H2
NAD+
NADH
O
HO
7
HO
PO3H2
O
HO
O
HO
9
1,3-bisphospho
glycerate
O
H2PO4
6
HO
H 2O
ATP
CH2 ADP
H2PO4
CH3
O
O
HO
Phosphoenol
pyruvate
O
10
HO
Pyruvate
6. Glyceraldehyde
phosphate isomerase
7. Phosphoglycerate
kinase
8. Phosphoglycerate
mutase
9. Enolase
10. Pyruvate kinase
O
Gliceraldehyde-3-phosphate to 1,3bisphosphoglycerate
Glyceraldehyde-3-phosphate
dehydrogenase
PO3H2
O
2x
PO 3H2
NAD+
O
NADH
HO
HO
O
O
Pi
H+
H2PO 3
D-glyceraldehyde3-phosphate
1,3-bisphosphoglycerate
Total ATP count: -2 ATP
Total NADH count: 2 NADH
1,3-bisphosphoglycerate to 3phosphoglycerate
PO 3H2
O
ADP
PO 3H2
ATP
2x HO
O
HO
O
Phosphoglycerate kinase
H2PO 3
O
HO
1.3-bisphosphoglycerate
3-Phosphoglycerate
2 ATP are synthesized
Total ATP count: 0 ATP
Total NADH count: 2 NADH
3-phosphoglycerate to 2phosphoglycerate
PO 3H2
O
2x
HO
HO
H2PO 3
O
O
Phosphoglycerate mutase
HO
HO
3-Phosphoglycerate
2-Phosphoglycerate
Total ATP count: 0 ATP
Total NADH count: 2 NADH
2-phosphoglycerate to
phosphoenolpyruvate
HO
CH2
H2O
H2PO 3
2x H2PO3
O
O
Enolase
HO
HO
2-Phosphoglycerate
Phosphoenolpyruvate
Total ATP count: 0 ATP
Total NADH count: 2 NADH
Phosphoenolpyruvate to pyruvate
CH2
2x
ADP
ATP
H2PO 3
CH3
O
O
O
Pyruvate kinase
HO
HO
Phosphoenolpyruvate
Pyruvate
2 ATP are synthesized
Total ATP count: 2 ATP
Total NADH count: 2 NADH
Glucose→Pyruvate
Total energy output
• 2 ATP are consumed
• 4 ATP are synthesized
• Total 2 ATP from 1 glucose
• 2 NADH are synthesized
• All ATP is synthesized without O2 (substrate-level
phosphorylation)
• Anaerobic glycolysis
Glucose→AcCoA→CO2+ H2O
Total energy output
• Total 2 ATP + 2 NADH from anaerobic glycolisis.
• 2 NADH from PDH
• 6 NADH+ 2 FADH2 from TCA
• 2 GTP from TCA
• Total 10 NADH+4 ATP + 2FADH2= 32 ATP
• All ATP is synthesized with O2 (oxidative
phosphorylation)
• Aerobic glycolysis
Glucose metabolism in cell
Glucose
Sequence of reactions
+
Aerobic Glycolisis
2x
CoA + CO2
Pyruvate
Anaerobic Glycolisis
Lactate
TCA, ETC, OP
32 ATP
2 ATP
Glycolysis regulation
Glucose
Glucose 6phosphatase
Hexokinase
Glucose-6-P
Fructose-6-P
Phosphofructo
kinase1 (PFK1)
Fructose-1,6bisphosphatase
AMP
AMP
ATP
Fructose-1,6-diP
Citrate
Acetyl-CoA
Inhibition
Activation
Pyruvate
carboxylase
Phosphoenol
pyruvate
Pyruvate
Pyruvate
kinase
ATP
Acetyl-CoA
Glycolysis regulation
• 3 enzymes catalyzing irreversible steps are
regulated:
1) Hexokinase
2) Phosphofructokinase-1
3) Pyruvate kinase
• Feedback or hormonal control
Hexokinase regulation
Feedback mechanism
PFK1 and PFK2.
Distinguish them.
PFK1
PFK2
• Only kinase activity
• Both kinase and phospatase
• Phosporylates F-6-P
activity
• Produces F-1,6-BP for further
• Regulates F-6-P and F-2,6-BP
glycolysis
amount
• Insulin activated
• F-2,6-BP doesn’t go to
• Glucagon inhibited
glycolisis
PFK1regulation. Feedback mechanism.
Pyruvate kinase regulation
Feedback mechanism
Hormonal control
• Insulin and glucagon are two main hormones
controlling glucose methabolism
• Insulin – fed state hormone
• Insuline provides glycolysis, glicogen and fatty
acid synthesis
• Glucagon – fasting state hormone
• Glucagon provides gluconeogenesis, glicogen
and fatty acids decomposition
Hormonal control over PFK1 and pyruvate kinase
Activation of glycolysis
Activation of gluconeogenesis
Fructose-1-P
Fructose-1-P
Glucagon
HO
HO
HO P O
Protein kinase-1
O
O
CH3
CH2 O
H HO
H
OH
OH H
ATP
P
Pi
PFK2
ADP
CH3
CH2 O
H HO
H
OH
OH H
ADP
ATP
FBPase-2
PFK2
Active
FBPase-2
Active H2O
O
-
HO P O
O
O P O
-
-
O P O
O
O
OH
Pi
O
H
HO
O
O P O
H
OH
H
-
H2O
-
OH
Fructose-2,6-diP
OH
Protein phosphatase-1
Insulin
O
H
HO
O
O P O
H
OH
H
OH
Fructose-2,6-diP
-
Aerobic and anaerobic glycolysis ATP
production
Glucose
Sequence of reactions
+
Aerobic Glycolisis
2x
CoA + CO2
Pyruvate
Anaerobic Glycolisis
Lactate
TCA, ETC, OP
32 ATP
2 ATP
Pyruvate fate
Anaerobic
(lactic acid fermentation
Aerobic Oxidation
Anaerobic
(alcoholic fermentation)
Lactate
Pyruvate
Ethanol
In mammals
Pyruvate to AcCoA
PDH
COOH
C O
Pyruvate dehydrogenase
+
S-CoA
C O
HS-CoA
CH3
CH3
NAD+
NADH
+
CO2
PDH regulation
Pyruvate to lactate
Pyruvate to oxaloacetate
• Pyruvate kinase reaction is irreversible
• In cytosol glucose and oxaloacetate can not be
synthesized from pyruvate
• Oxaloacetate is TCA intermediate
• If unsufficient can be synthesized from
pyruvate in mytochondria
• Catalyzed by pyruvatecarboxylase
Pyruvate carboxylase
HCO3
ATP
COOH
O
CH3
Aspartate
(transamination)
ADP+Pi
COOH
O
Citrate
(TCA cycle)
HO
O
Phosphoenolpyruvate
(gluconeogenesis)