PETER PAZMANY
SEMMELWEIS
UNIVERSITY
UNIVERSITY
Development of Complex Curricula for Molecular Bionics and Infobionics Programs within a
consortial* framework**
Consortium leader
PETER PAZMANY UNIVERSITY
Consortium members
SEMMELWEIS UNIVERSITY, DIALOG CAMPUS PUBLISHER
The Project has been realised with the support of the European Union and has been co-financed by
the European Social Fund ***
**Molekuláris bionika és Infobionika Szakok tananyagának komplex fejlesztése konzorciumi keretben
***A projekt az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósul meg.
2011.09.13..
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Semmelweis University
www.sote.hu
BIOCHEMISTRY
BIOKÉMIA
ANABOLISM OF CARBOHYDRATES
A SZÉNHIDRÁTOK SZINTÉZISE
TRETTER LÁSZLÓ
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BIOCHEMISTRY: ANABOLISM OF
CARBOHYDRATES
http://semmelweis-egyetem.hu/
Table of contents:
Gluconeogenesis and its regulation
Glycogen synthesis and its regulation
Lactose synthesis
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Learning objectives
At the end of the presentation students will be able:
To demonstrate the difference between the steps of
gluconeogenesis and glycolysis.
To demonstrate the reactions, specific for gluconeogenesis.
To understand the concept of gluconeogenesis i.e. that the
higher multicellular organisms use many noncarbohydrate
precursors for the biosynthesis of glucose, because the
maintenance of blood sugar level is highly important.
To understand the principles of metabolic regulation by the
comparison the regulation of gluconeogenesis and
glycolysis.
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
GluconeogenesisDEF: biosynthesis of glucose from
simpler, non-carbohydrate precursors
The most important precursors of gluconeogenesis:
lactate, pyruvate
glycerol
(glucogenic) amino acids
fatty acids with odd number of carbon atoms
Glucogenic amino acidsDEF: amino acids with carbon skeleton that can be used in
glucose synthesis during gluconeogenesis (e.g. alanine, aspartate)
Antonym: Ketogenic amino acidsDEF: amino acids with carbon skeleton that can be
used in ketone body synthesis during starvation (e.g. leucine, lysine)
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
The principles of gluconeogenesis I.
Gluconeogenesis requires reactions from glycolysis, citric acid
cycle and a few special reactions
The nonequilibrium reactions during glucose catabolism
obstruct the simple reversal of glycolysis
The nonequilibrium reactions:
1. phosphoenol pyruvate→pyruvate
2. fructose 6-P→fructose 1,6-P2
3. glucose→glucose 6-P
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
The principles of gluconeogenesis II.
The circumvention of glycolytic reactions
1. Glycolysis: phosphoenol pyruvate→pyruvate
Pyruvate kinase
ADP
ATP
Gluconeogenesis:pyruvate→oxaloacetate→phosphoenol pyruvate
Pyruvate carboxylase
CO2
ATP
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ADP+Pi
Phosphoenol yruvate
carboxykinase
GTP
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CO2
GDP
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
The principles of gluconeogenesis III.
The circumvention of glycolytic reactions
However: mitochondria are impermeable for oxaloacetate
but oxaloacetate should be present in the cytosol
in order to
become a substrate for phosphoenol pyruvate carboxykinase (PEPCK)
Problem solved by
- reversible oxidoreduction and transamination
- reversible transports
Malate dehydrogenase (MDH)
OA
MAL
NADH
OA
MAL
NAD+
transaminase
Glut
Malate dehydrogenase (MDH)
α KG
OA
NAD+
ASP
NADH
transaminase
ASP
α KG
OA
Glut
transaminasesDEF: enzymes catalyzing the reversible transfer of amino group
from an amino acid to an oxo acid resulting a new amino acid and a new oxo acid
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
The principles of gluconeogenesis IV.
The circumvention of glycolytic reactions
2. Glycolysis: fructose 6-P→fructose 1,6-P2
Phosphofructokinase I
ATP
ADP
Gluconeogenesis: Fructose 1,6-P2→ Fructose 6-P
Fructose 1,6-P2ase
H 2O
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
The principles of gluconeogenesis V.
The circumvention of glycolytic reactions
3. Glycolysis: glucose→glucose 6-P
Hexokinase
Glucokinase
ATP
ADP
Gluconeogenesis: glucose 6-P→glucose
Gl
Gl 6-Pase
Gl
Pi
Pi
Gl 6-P
Gl 6-P H2O
G6T
ER
Glucose 6-P is transported by glucose 6P transporter (G6T) then hydrolized in the ER by glucose 6Pase
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Gluconeogenesis in the liver from lactate and pyruvate
Gl
Gl6Pase
Gl
ER
Pi
Gl 6-P
Fr 6-P
Fr 1,6P2ase
Fr 1,6-P
PYR
TRIOSE PHOSPHATES
PYR
PEP
PEPCK
OA
ASP
OA
MAL
CELL MEMBRANE
LACTATE
LACTATE
Ac-CoA
ASP PYR
PC
OA
MALATE
TCA
CYCLE
MITO
CELL
MEMBRANE
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Entry of glycerol into the gluconeogenesis (Liver)
ADIPOSE
TISSUE
Gl
Gl6Pase
Gl
Gl 6-P
BLOOD
ER
Fr 6-P
Pi
Glycerol
Fr 1,6P2ase
Fr 1,6-P
Glycerol kinase
Glycerol
ATP
ADP
Aldolase
A
Aldolase
NADH
Dihydroxyacetone-P
B
CELL MEMBRANE
NAD
Glycerol 3-P
dehydrogenase
Glycerol 3-P
Glyceraldehyde 3-P
CELL
MEMBRANE
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Entry of fructose into the gluconeogenesis (Liver)
Gl
Gl6Pase
Gl
ER
Pi
Gl 6-P
Diet
Fr 6-P
Fructose
Fructose
Fr 1,6P2ase
Fr 1,6-P
Fructokinase
Fr 1-P
Aldolase A
Aldolase B
CELL MEMBRANE
Dihydroxyacetone-P
Glyceraldehyde 3-P
Aldolase B
ATP
Glyceraldehyde
Triokinase
CELL
MEMBRANE
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BIOCHEMISTRY: ANABOLISM OF
CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Entry of amino acids into the gluconeogenic pathway
Gl
Gl6Pase
Gl
ER
Serine
Pi
www.sote.hu
Gl 6-P
Fr 6-P
Fr 1,6P2ase
Fr 1,6-P
ALA
TRIOSE PHOSPHATES
PEP
PEPCK GOT
OA
ASP
MDH
MAL
PYR
LACTATE
Ac-CoA
ASP PYR
PC
OA
OA
MDH
MALATE
CELL MEMBRANE
TCA
CYCLE
Fumarate
MITO
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PYR
AMINO ACIDS
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α-KG
AMINO ACIDS
Succ-CoA
CELL
MEMBRANE
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BIOCHEMISTRY: ANABOLISM OF
CARBOHYDRATES
http://semmelweis-egyetem.hu/
Entry of glycerol into the gluconeogenesis (Liver)
www.sote.hu
ADIPOSE
TISSUE
Gl
Gl6Pase
Gl
Gl 6-P
BLOOD
ER
Pi
Fr 6-P
Glycerol
Glycerol
Fr 1,6P2ase
Fr 1,6-P
Glycerol kinase
ATP
ADP
Aldolase A
Aldolase B
CELL MEMBRANE
NADH
Dihydroxyacetone-P
NAD
Glycerol 3-P
dehydrogenase
Glycerol 3-P
Glyceraldehyde 3-P
CELL
MEMBRANE
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Entry of propionyl-CoA into the gluconeogenesis (Liver)
Fatty acids
with odd number
of carbon atoms
Valine
Isoleucine
Methionine
Cholesterol side
chain
Glucose
Propionyl-CoA
PEP
PEPCK
OA
Malate
Fumarate
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Succinyl-CoA
Succinate
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Regulation of gluconeogenesis
Gene expression
Covalent modification
Allosteric
Enzyme
Inducer
repressor
phosphorylat
ion
dephosphory
lation
activator
inhibitor
Pyruvate
carboxylase
Glucocort.
Glucagon
epinephrine
(cAMP)
insulin
-
-
-
-
Phosphoenol
pyruvate
carboxykinase
(PEPCK)
Glucocort.
Glucagon
epinephrine
(cAMP)
insulin
-
-
-
-
Fr 1,6-P2ase
Glucocort.
Glucagon
epinephrine
(cAMP)
-
-
-
Fructose 2,6-P2
AMP
Pyruvate kinase
Glucocort.
Glucagon
epinephrine
(cAMP)
-
-
Fructose 1,6-P2
ATP, alanine
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insulin
insulin
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Regulation at the PEPCK level
The promoter region of PEPCK gene
PEPCK (phosphoenol pyruvate carboxykinase) is the rate limiting
step of gluconeogenezis
All of the important hormones in the metabolism can regulate the
PEPCK expression
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Regulation at the fr 2,6-P2ase level (liver)
The elevation of [cAMP] increases the rate of
gluconeogensis and decreases the rate of
glycolysis in the liver
Glucagon
Receptor
Cell membrane
[cAMP]↑
PKA↑
G
+
L
Y
PFK2
PFK2 P
C
↑ Phosphatase↑ ↓ Kinase ↓
O
activity
activity
L Fr 6-P
Y
+
X
X
↓ [fr2,6-P2] ↓
S
I Fr 1,6-P2
S
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Glucose
Fr 6-P
Fr 1,6-P2
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G
L
U
C
O
N
E
O
G
E
N
E
S
I
S
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Regulation of gluconeogenesis I
Regulated steps:
pyruvate carboxylase
PEPCK
fr 2,6-P2ase
Gl 6-Pase
Pyruvate carboxylase is regulated step, it catalyses an irreversible
reaction, it is at the beginning of the pathway, but it is not entirely comitted to the
gluconeogenesis. Pyruvate carboxylase is also an anaplerotic enzyme of the citric
acid cycle. Anaplerotic reactions can not be entirely shut off.
AnapleroticDEF: a reaction which can replenish the supply of intermediates in a
metabolic pathway, e.g. in the citric acid cycle.
PEPCK is a rate limiting, irreversible, heavily regulated step at the initial
part of the pathway. It is important to note that neither allosteric nor phosphorylation
type of regulation has not been detected on the enzyme. It is regulated exclusively on
the gene expression level.
Rate limiting stepDEF: The slowest step in a metabolic pathway. Usually it is heavily
regulated. E.g. The rate limiting step of glycolysis is the fr 6-P fr1,6-P2 transformation.
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Regulation of gluconeogenezis II.
Fr 1,6-P2ase is also heavily regulated. This enzyme however, not the main regulatory
site of the gluconeogenesis. It is far from the beginning of the pathway. It is
particularly interesting that the regulation of PFK1 and the fr 1,6-P2ase is very much
coordinated. Those conditions and effectors which stimulate Fr 1,6-P2ase activity
inhibit PFK1 activity and vice versa. It is very tempting to say that because PFK1 is
the rate-limiting enzyme of the glycolysis, Fr 1,6-P2ase should be the rate-limiting
one of the gluconeogenesis, however it is not true.
Gl6-Pase is also regulated, but not the rate limiting step either. The reasons for that
1.
2.
It is at the very end of the pathway,
It is not entirely committed to the gluconeogenesis but playing a role in the
glycogenolysis as well. Glycogenolysis is activated earlier than gluconeogenesis, so
the enzyme is not suitable for the fine tuning of the gluconeogenesis.
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Gluconeogenesis
http://semmelweis-egyetem.hu/
Summary
Because of thermodinamic reasons gluconeogenesis is
not a simple reversal of glycolysis
The irreversible steps of glycolysis should be bypassed
The most important gluconeogenic precursors join to the
pathway at different levels
The regulation of glucogenesis occurs at the irreversible
reactions.
The most important regulatory site of gluconeogenesis is
the PEPCK enzyme
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
http://semmelweis-egyetem.hu/
Major anabolic and catabolic pathways in glucose metabolism
C
A
T
A
B
O
L
I
C
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A
N
A
B
O
L
I
C
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Learning objectives
At the end of the presentation students will
be able:
To demonstrate the difference between the
steps of glycogenesis and glycogenolysis.
To demonstrate the reactions, specific for
glycogenesis.
To understand the principles of
simultaneous and opposite regulation of
glycogenolysis and glycogenesis.
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Overview of glycogen synthesis
Glucokinase
Hexokinase
phosphoglucomutase
Gl 6-P
Glucose
ATP
ADP
Gl 1-P
Gl 1-P
uridyltransferase
UTP
UDP-glucose
PPi
H2O
Glucose (n)
Glycogen
synthase
UDP
Pi+Pi
Glucose (n+1)
Cost of glycogen synthesis: gluco-, hexokinase
uridyltransferase
Total cost
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1 ATP
1 UTP
2 ATP equivalent
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Initiation of glycogen synthesis,
The role of glycogenin
Glycogenin
Primed glycogenin
Self-glucosylating
Tyr-OH
8 UDP-gluc
Glycogen synthase
and
Branching enzyme
Tyr-O-(glucose)8
8 UDP
n UDP-gluc
Glycogenin-Glycogen complex
Tyr-O-(glycogen
n UDP
Glycogen synthase cannot initiate synthesis without having a primer
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
The role of branching enzyme in the synthesis
4
Glycogen
synthase
7UDP-gl
4
4
4
4
7UDP
1
11
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Branching
enzyme
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Regulation of glycogen synthesis I
Main regulator: reversible phosphorylation/dephosphorylation
cAMP
Ca2+
+
+
Protein kinases
+
Glycogen synthase a ATP
active
Pi
ADP
H2O
Glycogen synthase b
inactive
P
+
Phosphoprotein
phosphatase
+
-
Insulin
2011.09.13..
Gl 6-P
cAMP
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Cyclic AMP
Secondary messengerDEF: An effector
molecule synthesized within the cell in
response to an external signal (first
messenger) such as a hormone
Cyclic AMP (cAMP) is formed from
ATP by the adenylate cycle
enzyme. First messengers, which
could elevate cAMP level are
glucagon, adrenalin on beta 1,2
receptors, ACTH etc.
cAMP can activate protein kinase-A
which can initiate a cascade of
phosphorylation
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Regulation of glycogen synthesis II
Elevation of [cAMP], or [Ca2+] in the liver indicates the presence of glucagon and
adrenaline.
Meaning of glucagon: hypoglycemia, glycogen should be mobilized
Glycogenesis should be inactivated.
Meaning of adrenaline “fight or fly” stress, glycogen should be mobilized,
glycogenesis should be inactivated
cAMP, Ca2+, activate protein kinases which phosphorylate glycogen synthase
Phosphorylated glycogen synthase is inactive – synthesis stopped
Phoshatases could remove the phosphorylation (inhibition) of the enzyme.
cAMP inhibits the phosphatase, maintains phosphorylation of glycogen synthase
(GS), maintains inhibition of the synthesis
Insulin stimulates the phosphatase, relieves GS from inhibition, stimulates
synthesis
Gl 6-P precursor of the glycogen synthesis stimulates the inactive GS.
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Glucose stimulates glycogen synthesis in the liver
www.sote.hu
Increased blood glucose stimulates glycogen synthesis in the liver in
an insulin independent manner as well.
Glucose binds to phosphorylase a, and glucose-bound phosphorylase
is a better substrate for phosphoprotein phosphatase.
Phosphorylase acts as a glucose receptor. Glucose promotes
inactivation of phosphorylase thus inhibits glycogenolysis.
However glycogen synthesis should also be stimulated.Active
phosphorylase inhibits dephosphorylation of GS by protein
phosphatase. But only phosphorylase a can inhibit this
process.Conversion of phosphorylase a to b relieves the inhibition, GS
will be dephosphorylated, active, glycogen synthesis could start.
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Glucose stimulates glycogen synthesis in the liver
PP=phosphoprotein phosphatase
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
Glycogen synthesis
http://semmelweis-egyetem.hu/
Summary
As gluconeogenesis is not the reversal of glycolysis, glycogen
synthesis is also not the reversal of glycogenolysis.
Glycogen synthesis needs energy, 2 high energy phosphate
required/glucose incorporated into glycogen.
Glycogen synthase is unable to prime “de novo” glycogen synthesis, In
order to create a new glycogen molecule, a primer is needed, This
primer is the self-catalytic glycogenin protein.
The glycogen synthesis is regulated both by reversible
phosphorylation/dephosphorylation, both by allosteric effectors. Among
the allosteric effectors in the liver, the glucose is the most important.
Glucose is able to stimulate glycogen synthesis in the liver in the
absence of insulin as well.
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
http://semmelweis-egyetem.hu/
Lactose synthesis
LactoseDEF: The disaccharide of the milk, containing glucose and galactose
Lactose synthesis: in lactating mammary gland
The enzyme:galactosyltransferase catalyzed reaction
UDP-galactose + N-acetyl-glucosamine → Dgalactosyl-N-acetyl-glucosamine
protein attached
This enzyme has a role in the glycoprotein synthesis
The enzyme does not accept glucose as a galactose acceptor.
However, after delivery the specificity of the enzyme changes
UDP-galactose + glucose → lactose + UDP
lactose synthase
Reason for change in the specificity: lactalbumin: produced by the mammary gland upon hormonal
influence. Lactalbumin changes substrate specificity of galactosyltransferase.
Lactalbumin-galactosyltransferase complex = lactose synthase
GlycoproteinDEF: Proteins containing carbohydrate groups
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Biochemistry: Anabolism of carbohydrates
http://semmelweis-egyetem.hu/
Recommended literature
Orvosi Biokémia (Ed. Ádám Veronika)
2011.09.13..
Textbook of Biochemistry
Ed. Thomas Devlin 5th-7th edition
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
http://semmelweis-egyetem.hu/
Questions:
1. Which allosteric regulators can regulate both the glycolysis
and the gluconeogenesis?
2. How would influence the elevation of cAMP the
gluconeogenesis
3. Which reactions require ATP in gluconeogenesis starting from
lactate
4. Which enzymes are active in phosphorylated form in the
glycogen metabolism.
5. What is the effect of insulin on the gluconeogenesis?
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BIOCHEMISTRY: ANABOLISM OF CARBOHYDRATES
http://semmelweis-egyetem.hu/
Questions:
Which statements are true for the synthesis of glycogen?
1. Glycogen synthase reaction connects free glucose molecules
2. Glycogen synthase requires ATP for the catalysis
3. During synthesis inorganic phosphate will be incorporated into the glycogen
4. The source of incorporated glucose is UDP-glucose
5. Branches are formed as postsynthetic modifications
A:1,2,3,
B:2,4
C:1,5,
D:4,5
E:4
Which statements are true for the regulation of glycogen metabolism?
1. Phosphorylation stimulates glycogen phosphorylase activity
2. Phosphorylation decreases the activity of glycogen synthase
3. Phosphorylation increases the activity of glycogen synthase
4. Calcium increases the activity of phosphorylase kinase
5. Glucose decreases the activity of glycogen synthase in liver
A:1,2,5,
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B:1,2,4,
C:2,3,5,
D:3,4,5
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