the sweet side of catabolism: carbohydrates as cellular fuels russian national research medical...
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The sweet side of catabolism: carbohydrates as cellular fuels
Russian National Research Medical University
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
Maltose Sucrose Lactose
Digestion byamylase
Monosaccharides
2xGlucose Glucose+Fructose Glucose+Galactose
Maltase Sucrase Lactase
Absorption of carbohydrates• Process of monosacharides transport from gut to blood stream or lymph• Involves special transporting proteins located on membrane of intestine cells
DigestionComposition 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
Pyruvate
AcetylCoa
CO2 + H2O + ATP
TCA
Aerobic Glycolisis
ETC+OP
Lactate
Anaerobic Glycolisis
TCA
Glycolisis
1. Glucokinase2. Phosphogluco isomerase3. Phosphofructo kinase-14. Aldolase5. Triosophosphate isomerase
O
OH
HH
H
OH
OH
H OH
H
OH
O
OH
H
OH
OH
H
H
O OH
O-
O-O
P
O
OH
H
OH
OH
H
H
O O
O-
O-O
P O-
O-O
P
OPO3H2
OH
O
OPO3H2
O
OH
O
OH
HH
H
OH
OH
H OH
H
O
O-
O-O
P
OPO3H2
OH
O
OH
CH3O
O
OH
Glucose Glucose-6-P Fructose-6-P Fructose-1,6-diP
ATP ADP ATP ADP
1 2 3
4
5
67
8
9
10
6. Glyceraldehyde phosphate isomerase7. Phosphoglycerate kinase8. Phosphoglycerate mutase9. Enolase10. Pyruvate kinase
OPO3H2
OH
O
H2PO4
OH
H2PO4O
OH
CH2H2PO4
O
OH
1,3-bisphosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
ATP ADP
H2OADP ATP
NAD+NADH
Phosphoenolpyruvate Pyruvate
Sequence of reactions
+Pyruvate
Glucose
Glucose metabolism in cell
Anaerobic Glycolisis
CoA2x + CO2
Aerobic Glycolisis
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 Glucokinase
• Low Km value
• High affinity to glucose
• Located in most tissue cells
• Three isoforms (I, II, III)
• High Km value
• Low affinity to glucose
• Located mostly in liver cells
•Actually IV isoform of hexokinase
Glucose-2-18F
• 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.
1. Glucokinase2. Phosphogluco isomerase3. Phosphofructo kinase-14. Aldolase5. Triosophosphate isomerase
O
OH
HH
H
OH
OH
H OH
H
OH
O
OH
H
OH
OH
H
H
O OH
O-
O-O
P
O
OH
H
OH
OH
H
H
O O
O-
O-O
P O-
O-O
P
OPO3H2
OH
O
OPO3H2
O
OH
O
OH
HH
H
OH
OH
H OH
H
O
O-
O-O
P
Glucose Glucose-6-P Fructose-6-P Fructose-1,6-diP
ATP ADP ATP ADP
1 2 3
4
5
Dyhydroxyacetonephosphate
D-glyceraldehyde -3-phosphate
Glucose to glucose-6-P
1st ATP is hydrolysed
Total ATP count: -1 ATPTotal NADH count: 0 NADH
Glucose-6-P to fructose-6-P
Total ATP count: -1 ATPTotal NADH count: 0 NADH
O
H
H
OH
H
OH
OH
HOH
H
OP
O
O
OOP
O
O
OO
H
OH
H
H
OH
CH2OH
OH
Phosphohexose isomerase
Fructose-6-P to fructose-1,6-diP
2nd ATP is hydrolysed
Total ATP count: -2 ATPTotal NADH count: 0 NADH
PO
OH
OH O
OH
H
OH
OH
H
H
H2C OHO
OH
H
OH
OH
H
H
P P
OH
OH
O OHO
OH
Phosphofructokinase-1
ATP ADP
Fructose-6-P Fructose-1,6-diP
Fructose-2,6-diP to gliceraldehyde-3-phosphate and dihidroxyacetone-phosphate
Total ATP count: -2 ATPTotal NADH count: 0 NADH
O
OH
H
OH
OH
H
H
P P
OH
OH
O OHO
OH
OPO3H2
O
OH
OPO3H2
OH
O
Aldolase
Fructose-2,6-diP
Dyhydroxyacetonephosphate
D-glyceraldehyde-3-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.
OPO3H2
OH
O
OPO3H2
OH
O
OH
CH3O
O
OH
67
8
9
10
OPO3H2
OH
O
H2PO4
OH
H2PO4O
OH
CH2H2PO4
O
OH
1,3-bisphosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
ATP ADP
H2O
ADP ATP
NAD+NADH
6. Glyceraldehyde phosphate isomerase7. Phosphoglycerate kinase8. Phosphoglycerate mutase9. Enolase10. Pyruvate kinase
Phosphoenolpyruvate Pyruvate
Gliceraldehyde-3-phosphate to 1,3-bisphosphoglycerate
2x
Total ATP count: -2 ATPTotal NADH count: 2 NADH
OPO3H2
OH
O
NAD+ NADH
Pi H+
Glyceraldehyde-3-phosphate dehydrogenase
OPO3H2
OH
O
H2PO3D-glyceraldehyde-3-phosphate
1,3-bisphosphoglycerate
1,3-bisphosphoglycerate to 3-phosphoglycerate
2x
Total ATP count: 0 ATPTotal NADH count: 2 NADH
2 ATP are synthesized
OPO3H2
OH
O
H2PO3
OPO3H2
OH
O
OH
1.3-bisphosphoglycerate
ADP ATP
Phosphoglycerate kinase
3-Phosphoglycerate
3-phosphoglycerate to 2-phosphoglycerate
2x
Total ATP count: 0 ATPTotal NADH count: 2 NADH
OPO3H2
OH
O
OH
3-Phosphoglycerate
OH
H2PO3O
OH
Phosphoglycerate mutase
2-Phosphoglycerate
2-phosphoglycerate to phosphoenolpyruvate
2x
Total ATP count: 0 ATPTotal NADH count: 2 NADH
OH
H2PO3O
OH
2-Phosphoglycerate
H2O CH2
H2PO3
O
OH
Phosphoenolpyruvate
Enolase
Phosphoenolpyruvate to pyruvate
2x
Total ATP count: 2 ATPTotal NADH count: 2 NADH
2 ATP are synthesized
CH2
H2PO3
O
OH
Phosphoenolpyruvate
CH3
O
O
OH
ADP ATP
Pyruvate kinase
Pyruvate
Glucose→PyruvateTotal 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+ H2OTotal 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
Sequence of reactions
+ Pyruvate
Glucose
Glucose metabolism in cell
Anaerobic Glycolisis
CoA2x + CO2
Aerobic Glycolisis
TCA, ETC, OP
Lactate
32 ATP 2 ATP
Glycolysis regulationGlucose
Glucose-6-P
Fructose-6-P
Fructose-1,6-diP
Phosphoenolpyruvate
Pyruvate
HexokinaseGlucose 6-phosphatase
Fructose-1,6-bisphosphatase
Phosphofructokinase1 (PFK1)
Pyruvatecarboxylase
Pyruvatekinase
AMP
ATP
Citrate
ATP
Acetyl-CoA
AMP
Acetyl-CoA
Inhibition
Activation
Glycolysis regulation
• 3 enzymes catalyzing irreversible steps are
regulated:
1) Hexokinase
2) Phosphofructokinase-1
3) Pyruvate kinase
• Feedback or hormonal control
Hexokinase regulationFeedback mechanism
PFK1 and PFK2.Distinguish them.
• Only kinase activity
• Phosporylates F-6-P
• Produces F-1,6-BP for further
glycolysis
• Insulin activated
• Glucagon inhibited
• Both kinase and phospatase
activity
• Regulates F-6-P and F-2,6-BP
amount
• F-2,6-BP doesn’t go to
glycolisis
PFK1 PFK2
PFK1regulation. Feedback mechanism.
Pyruvate kinase regulationFeedback 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
CH3
POH
OH
O
O
O
OHH
OH
OH
H
CH2
H
OHO
O
H
OH
OH
H
H
O
O-
O-O
P
OH
O-
O
P
PFK2FBPase-2
FBPase-2 PFK2 FBPase-2
CH3
POH
OH
O
O
O
OHH
OH
OH
H
CH2
H
OHO
O
H
OH
OH
H
H
O
O-
O-O
P
OH
O-
O
P
ATP
ADP
ATP ADP
H2O
Pi
Active Active
P
H2OPi
Protein kinase-1
Protein phosphatase-1
Glucagon
Insulin
Activation of gluconeogenesisActivation of glycolysis
Fructose-1-P
Fructose-2,6-diP Fructose-2,6-diP
Fructose-1-P
Sequence of reactions
+ Pyruvate
Glucose
Aerobic and anaerobic glycolysis ATP production
Anaerobic Glycolisis
CoA2x + CO2
Aerobic Glycolisis
TCA, ETC, OP
Lactate
32 ATP 2 ATP
In mammals
Anaerobic(lactic acid fermentation
Aerobic Oxidation Anaerobic(alcoholic fermentation)
Lactate Pyruvate Ethanol
Pyruvate fate
Pyruvate dehydrogenase
NAD+ NADH
COOH
CH3
O HS-CoA
S-CoA
CH3
O CO2+C C +
Pyruvate to AcCoAPDH
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
O
OH
COOH
O
O
CH3
COOH
HCO3ATP ADP+Pi
Aspartate (transamination)
Citrate (TCA cycle)
Phosphoenolpyruvate(gluconeogenesis)