Download Chapter6 Carbohydrate Metabolism

Chapter 6
Carbohydrate Metabolism
Jia-Qing Zhang 张嘉晴
Biochemistry department
Medical college Jinan university
Mar. 2007
1
What’s metabolism?
2
Metabolism…..
What is Life?
What are the properties of life?
Movement
Reproduction of one’s kid
Metabolism
3
Carbohydrate
metabolism
Lipid
metabolism
Protein
metabolism
4
5
metabolism
Carbohydrate
metabolism
Metabolism
of lipid
Catabolism
of protein
6
Carbohydrate Metabolism
7
Section 1 Introduction
Carbohydrates are the major source of carbon
atoms and energy for living organisms.
8
Carbohydratesf of the diet
Starch
Sugar
Lactose
cellulose
9
Starch
Sugar
Cellulose
10
Glucose, the hydrolyzed product of most starch,
will be focused in this chapter.
11
Glucose transport
12
The fate of absorbed glucose
13
Section 2 Anaerobic
degradation of glucose
Glycolysis
Pyruvate
or lactate
Glucos
e
AT
P
cytosol
14
2.1 Basic process of glycolysis
Glucos
e
Phase 1
Pyruvat
e
Phase 2
Lactate
15
Phase1 Pyruvate formation from glucose
Reaction1
Glucose-6Phosphate
Glucose
Hexokinase
16
Hexokinase
CH2OH
O
CH2OPO3
O
OH
OH
17
Hexokinases
Hexokinases is a key enzyme in glycolysis and have 4 isoenzymes ,
isoenzyme 4 present in liver, and named glucokinase.
1
Hexokinases in
all extrahepatic
cells
2
3
4
Glucokinase present
in liver
18
Hexokinase has a low Km 0.1mol/L,
high affinity for glucose.
Hepatic glucokinase has high Km > 10mol/L,
a low affinity for glucose
19
Glucose-6-Phosphate
Reaction 2:
Glucose-6Phosphate
Fructose-6Phosphate
Phosphohexose
isomerase
20
Phosphohexose isomerase
CH2OPO3
O
OH
CH2OPO3
O CH2OH
OH
21
Reaction 3:
Fructose-6Phosphate
Fructose-1,6Phosphate
Phosphofructokinase
CH2OPO3
O CH2OH
OH
CH2OPO3
O CH2OPO3
OH
22
Phosphofructokinase
Phosphofructokinase
23
helpful
Reaction 4:
Fructose-1,6Phosphate
Glyceraldehyde 3Phosphate
+
Dihydroxyacetone
Phosphate(DHAP)
Aldolase
CH2OPO3
C=O
CH2OH
CHO
H-C-OH
CH2OPO3
24
Aldolase
25
Reaction 5:
Glyceraldehy
de
3-Phosphate
+
2×
Glyceraldehyde
3-Phosphate
Dihydroxyace
tone
Phosphate Triose Phosphate Isomerase
26
Triose Phosphate Isomerase
27
Reaction 6:
Glyceraldehyde
3-Phosphate
CHO
H-C-OH
CH2OPO3
1,3Bisphosphoglycerate
Glyceraldehyde
3-Phosphate
Dehydrogenase
O
C ~OPO3
High energy
H-C-OH
CH2OPO3
28
Glyceraldehyde 3-Phosphate Dehydrogenase
29
Reaction 7:
1,3Bisphosph
oglycerate
O
C ~OPO3
H-C-OH
Substrate level phosphorylation
3Phosphoglycerate
Phosphoglycerate Kinase
COO
H-C-OH
CH2OPO3
CH2OPO3
30
Phosphoglycerate Kinase
31
Reaction 8:
3Phosphoglycerate
COO
H-C-OH
CH2OPO3
2Phosphoglycerate
Phosphoglycerate Mutase
COO
H-C-OPO3
CH2OH
32
Mutase
33
Reaction 9:
2-Phosphoglycerate
COO
H-C-OPO3
CH2OH
Phosphoenolpyruvate
Enolase
COO
C~OPO3 PEP
CH2
High energy
34
Enolase
35
Reaction 10:
Phosphoenolpyruvate
COO
Pyruvate Kinase
Pyruvate
COO
C~OPO3 PEP
C=O
CH2
CH3
36
Pyruvate Kinase
37
O2
Glucose
CO2 + H2O
pyruvate
no O2
lactate
38
Conversion of pyruvate to lactate
39
Conversion of pyruvate to lactate
NADH +
H+
NAD+
Pyruvate
Lactate
Lactate dehydrogenase(LDH)
COO NADH + H+ COO
C=O
HO-C-H
CH3
L-lactate
NAD+
CH3
Pyruvate
40
How many ATP are produced in above
process?
2?
4?
Net ATP in glycolysis is 2
41
The features of the glycolysis
pathway






Major anaerobic pathway in all cells
NAD+ is the major oxidant
Requires PO4
Generates 2 ATP’s per glucose oxidized
End product is lactate (mammals)
Connects with Krebs cycle via pyruvate
42
43
44
2.2 Regulation of Glycolysis
45
46
6-phosphofructokinase-1
47
6-phosphofructokinase-1(PFK-1)
Allosteric enzyme
negative allosteric effectors
Citrate , ATP
Positive allosteric effectors
AMP, fructose1,6-bisphosphate, fructose2,6-bisphosphate

Response to changes in energy state of the
cell (ATP and AMP)
48
49
,
, is a potentially positive
Fructose-2,6-bisphosphate
effector of PFK-1.
Fructose-2,6-bisphosphate formed by
phosphorylation of Fructose--6-PO4 catalyzed by PFK-II.
50
Regulation of Pyruvate Kinase
51
52

Allosteric enzyme
Inhibited by ATP. alanine
Activated by fructose 1,6 bisphosphate

Regulated by phosphorylation and
Inactive
Active
dephosphorylation
PO4
enzyme
53
Regulation of Hexokinase
Allosteric enzyme
Inhibitor: Glucose-6-phosphate except for glucokinase
54
The Energy Story of Glycolysis
Glucose + 2ADP + 2Pi + 2NAD+
2 Pyruvate + 2ATP + 2NADH + 2H+ + 2H2O
Overall ANAEROBIC (no O2)
2Pyruvate + 2NADH
Lactate + 2NAD+
Overall AEROBIC(O2)
2NADH
5 ATPs
Oxidative phosphorylation
55
The Significance of Glycolysis


Glycolysis is the emergency energyyielding pathway----ineffient
Main way to produce ATP in some tissues
red blood cells, retina, testis, skin, medulla of kidney

In clinical practice
acidosis
56
Section 3
Aerobic Oxidation of Glucose
1.
Oxidation of glucose to pyruvate in cytosol
2.
Oxidation of pyruvate to acetylCoA in
mitochondria
3.
Tricarboxylic acid cycle and oxidative
phosphorylation
57
Oxidation of pyruvate to acetylCoA
Pyruvate + CoA
Acetyl CoA
+ CO2
Pyruvate
dehydrogenase complex
mitochondria
This reaction is irreversible.
58
Pyruvate dehydrogenase complex
Comprises of 3 kinds of enzyme and 5 cofactors:
E1: pyruvate dehydrogenase
E2:dihydrolipoyl transacetylase
E3:dihydrolipoyl dehydrogenase
Cofactors:
Thiamine pyrophosphate(TPP), FAD, NAD, CoA
and lipoic acid.
59

60
Pyruvate Dehydrogenase Complex
Acetyl-CoA
..
HS-CoA
C-CH3
O
..
CH3-C
O
acetyl
..
CH3-C
NAD+
TPP
E1
E2
E3
FAD H2
..
NADH ..
OH
hydroxyethyl
Pyruvate Dehydrogenase
Dihydrolipoyl
Transacetylase
Dihydrolipoyl
dehydrogenase
61
Tricarboxylic Acid Cycle
62
All Mean the Same
63
64
CH3C ~ S-CoA
CARBON BALANCE
O
4 Oxaloacetate
4 Malate
4 Fumarate
Citrate 6
2 carbons in
2 carbons out
Isocitrate 6
CO2
a-ketoglutarate 5
TCA cycle
CO2
4 Succinate
Succinyl-CoA 4
8 reactions
65
Reaction 1.
Oxaloacetate
+
Acetyl CoA
Citrate
+
Citrate Synthase
Coenzyme A
66
CH3-C~SCoA
O
Citrate Synthase
COO-
COOC=O
CH2
HS-CoA
-OOC-CH
2- C-OH
CH2 COO-
COO-
Oxaloacetate
(OAA)
CH2COOHO-C-COO-
Acetyl-CoA
CH2COO-
Citric Acid or Citrate
67
68
Reaction 2
Isocitrate
Citrate
Aconitase
69
Isocitrate Formation
CH2COO-H2O
HO-C-COOH-C-COOH
Citrate
CH2COOC-COO-
+H2O
H C-COO-
cis-Aconitate
CH2COOH-C-COO-
HO-C-COOH
Isocitrate
Aconitase
70
71
Reaction 3
Isocitrate
a-Ketoglutarate
+
Carbon Dioxide
Isocitrate Dehydrogenase
72
CH2COOH-C-COO-
CO2
HO-C-COOH
NAD+ NADH + H+
Isocitrate
COOCH2
CH2
C=O
COO-
a-Ketoglutarate
Isocitrate Dehydrogenase
73
74
Reaction 4
a-Ketoglutarate
+ CoA
Succinyl CoA +
Carbon Dioxide
a-Ketoglutarate Dehydrogenase
75
COOCH2
CH2
C=O
NAD+
FAD
Lipoic acid
HS-CoA
TPP
COO-
a-Ketoglutarate
CO2
COOCH2
CH2
C~SCoA
O
Succinyl-CoA
a-Ketoglutarate
dehydrogenase
Complex
76
ketoglutarate
77
Reation 5
Succinyl CoA
Succinate + CoA
Succinyl CoA Synthetase
78
Thioester bond energy conserved as GTP
COOCH2
CH2
C~SCoA
O
Pi
+
GDP GTP
Succinyl-CoA
HS-CoA
COOCH2
CH2
COO-
Succinate
Succinyl-CoA Synthetase
79
80
Reaction 6
Succinate
Fumarate
Succinate Dehydrogenase
81
82
Reaction 7
Malate
Fumarate
Fumarase
83
84
Reaction 8
Malate
Oxaloacetate
Malate Dehydrogenase
85
86
FAD
FADH2
NAD+
NADH + H+
H2O
COOH
COOH
C
C
C
H C
COOH
Succinate
H
COOH
COOH
C OH
C=O
H C
COOH
Fumarate
COOH
Malate
C
COOH
Oxaloacetate
87
CH3C ~ S-CoA
CARBON BALANCE
O
4 Oxaloacetate
4 Malate
4 Fumarate
Citrate 6
2 carbons in
2 carbons out
3 NADH
1 FADH2
Isocitrate 6
CO2
a-ketoglutarate 5
CO2
4 Succinate
Succinyl-CoA 4
GTP
88
ATP Generated in the Aerobic
Oxidation of Glucose

There are two ways for producing ATP
Substrate level phosphorylation
Succinyl CoA to succinate
Oxidative phosphorylation
89
3.2 ATP Generated in the Aerobic
Oxidation of Glucose

In aerobic oxidation of glucose
Gycolysis: 2 NADH and 2ATP produced by substrate level
phosphorylation
Production of acetylCoA: 2 NADH
TCA cycle: 2 ×3NADH ,2× 1 FAD and 2GTP
Stoichiometry: 2.5 ATP per NADH
1.5 ATP per FADH
Table 6-1
32 ATP are produced for one glucose
90
Features:
Acetyl-CoA enters forming citrate
3 NADH, 1 FADH2, and 1 GTP are formed
Oxaloacetate returns to form citrate
91
3.3 the regulation of aerobic oxidation of
glucose
The regulation of pyruvate
dehydrogenase complex
The regulation of
tricarboxylic acid cycle
92
Regulation of Pyruvate Dehydrogenase
complex
Pyruvate + HS-CoA + NAD+  Acetyl-CoA + NADH + H+
Activators:
Inhibitors
High NADH means that the cell is experiencing a
surplus of oxidative substrates and should not produce
more. Carbon flow should be redirected towards synthesis.
High Acetyl-CoA means that carbon flow into the Krebs cycle
is abundant and should be shut down and rechanneled
towards biosynthesis
93
Mechanism:
1. allosteric regulation
NADH and acetyl-CoA
2. Covalent Modification
E-1 subunits of PDH complex is subject to phosphorylation
TPP
Active
FAD
HPO4=
1
2
Insulin
3
E1-OH
PDH
phosphatase
H2O
ATP
PDH
kinase
E1-OPO3
ADP
Epinephrine
Glucagon
Cyclic-AMP
protein kinase
ATP
Inactive
94
Regulation of the Citric Acid Cycle
Key enzymes :
1. Citrate synthase
2. Isocitrate dehydrogenase
3. α-ketoglutarate dehydrogenase complex
Modulators:
The ratios of [NADH]/[NAD] and [ATP]/[ADP], high ratios inhibit
Additonally, Ca2+ is an activitor
Succinyl CoA is a inhibitor
summary
of TCA
95
Pentose Phosphate Pathway
96
PENTOSE PHOSPHATE Pathway
Take Home: The PENTOSE PHOSPHATE pathway is
basically used for the synthesis of NADPH and D-ribose.
It plays only a minor role (compared to GLYCOLYSIS)
in degradation for ATP energy.
97
The primary functions of this pathway are:
1. To generate NADPH,
2. To provide the cell with ribose-5-phosphate.
98
NADPH differs from NADH physiologically :
1)its primary use is in the synthesis of metabolic
intermediates (NADPH as reductant provides the
electrons to reduce them),
2) NADH is used to generate ATP
99
Basic Process


Found in cytosol
Two phases
Oxidative phase
nonreversible
Nonoxidative phase
reversible
100
101
102
The significance of PPP
1) Ribose 5- phosphate:
Ribose 5- phosphate is the starting pointing for the
synthesis of the nucleotides and nucleic acids.
103
2) NADPH:
a. NADPH is very important ”reducing power”for
synthesis of fatty acids and cholesterol, and the synthesis
of amino acids via glutamate dehydrogenase.
b. In erythrocytes, NADPH is the coenzyme of
glutathione reductase to keep the normal level of reduced
glutathione
Additonally, NADPH serves as the coenzyme of mixed
funtion oxidases.
104
Glycogen Formation and
Degradation
105
Location of glycogen
Glycogen is the storage form of glucose in animals and humans
Glycogen is synthesized and stored mainly in the liver and the
muscles
106
Features:
The structure of glycogen consists of long polymer
chains of glucose units connected by an alpha
glucosidic bonds.
All of the monomer units are alpha-D-glucose,
93%
of glucose units are joined by a-1,4-glucosidic
bond
7% of glucosyl residues are joined by a-1,6-glucosidic
bonds
Fig.6-11
107
108
109
Main chains: branch point every 3 units on average.
Branch: 5-12 glucosyl residues.
Two properties of this structure:
1) High solubility.
many terminals
4 hydroxyl groups
2) More reactive points for synthesis and degradation of
glycogen.
110
Glycogen Formation (glycogenesis)
Occurs in cytosol of liver and skeletal muscle
Dived into 3 phases:

ACTIVATION OF D-GLUCOSE

GLYCOSYL TRANSFER

BRANCHING
111
1.
Glucose
Glucose-6Phosphate
Glucokinase(liver
Hexokinase(muscle)
phosphoglucomutase
Glucose-1-phosphate
112
UDP-GLUCOSE
ACTIVATION:
G-1-P + UTP
UDP-GLUCOSE + PPi
UDP-Glucose pyrophosphorylase
2 Pi
O
CH2OH
O
H
HO
OH H
H
OH
HN
O
O
O
O P O P
O
O
N
O CH2
O
HO
Uridine diphosphate (UDP) Glucose
OH
113
O
CH2OH
H
HO
O
HN
O
OH H
GLYCOSYL TRANSFER
O
O
N
UDPG
O P O P O CH2
O
H OH
O
O
HO
OH
CH2OH
O
H
HO
CH2OH
OH H
H
OH H
O
H OH
NEW
H
HO
O
OH H
H OH
H
O
H OH
NON-REDUCING
END
CH2OH
O
OH H
O
H OH
CH2OH
CH2OH
O
H
O
O
OH H
O
H OH
114
115
BRANCHING
Cleave
Glycogenin
a1.,4->1,6-glucantransferase
116
GLYCOGEN SYNTHESIS ENZYMES

UDP-glucose pyrophosphorylase


Glycogen Synthase


forms UDP-glucose
major polymerizing enzyme
a1.,4->1,6-glucantransferase
117
Glycogen Degradation
(Glycogenolysis)
Glycogenolysis is not the reverse of glycogenesis
118
Glycogen Synthesis
Glycogen
Degradation
Glucose-6-PO4
Glucose-1-PO4
Synthesis
UDP-Glucose
glucose
119
Phosphorylase and Debranching Enzyme
Highly branched core
Phosphorylase
Phosphorylase
Phosphorylase
G-1-p
Glycogen
Debranching enzyme1
Limit Branch
Debranching enzyme2
+
D-glucose
Debranching enzyme: a tandem enzyme
Oligo α1,4 α 1,4 glucantransferase
Transfer a trisaccharide unit
glucosidase
Hydorlyze a 1,6 branch point
121
Glycogen Breakdown
Glycogen
Phosphorylase and
PO4
Debranching Enzyme
Glucose-1-Phosphate
Phosphoglucomutase
Glucose-6-Phosphate
Glucose
Glycolysis
Take home: Glycogen contributes glucose to glycolysis and
to blood glucose (Liver)
122
The regulation of glycogensis and
glycogenolysis
123
Regulatory site of glycogenesis and
glycogenolysis:
•Phosphorylase
•Glycogen synthase
124
Phosphorylase
Phosphorylase
G-1-p
125
Glucagon,epinephrine
Inactive
Adenylate cyclase
PKA
protein kinase A
cAMP
b
Phosphoryl
ase b
kinase
Phosphoryl
ase b
kinase
inactive
a
Active
Phosphorylase
126
127
Glycogen synthase
128
Glycogen
+
Glycogen synthase
+
129
Glucagon,epinephrine
active
Adenylate cyclase
a
PKA
protein kinase A
cAMP
b
inactive
Glycogen synthase
130
Glucagon,epinephrine
Adenylyl cyclase
PKA
protein kinase A
cAMP
synthase
phosphorylase
b
b
inactive
Phosphorylating inhibitor-1
Active
Protein
phosphatase-1
131
Active
inactive
132
Allosteric regulation:
Phosphorylase:
Activitor: AMP
Inhibitor: ATP, glucose-6-phosphate
Glycogen synthase:
Activitor: ATP, Glucose-6-phosphate
133
TAKE HOME:
DEGRADATION
What activates glycogen degradation
inactivates glycogen synthesis.
SYNTHESIS
What activates glycogen synthesis
inactivates glycogen degradation
134
The Significance of Glycogenesis
and Glycogenolysis

Liver
maintain blood glucose concentration

Skeletal muscle
fuel reserve for synthesis of ATP
135
Glycogen Storage Diseases

Deficiency of
glucose 6-phosphatase
liver phosphorylase
liver phosphorylase kinase
branching enzyme
debranching enzyme
muscle phosphorylase
Table 6-2
136
Gluconeogenesis
Gluconeogenesis:The process of transformation
of non-carbohydrates to glucose or glycogen
glucogenic amino acids
lactate
glycerol
organic acids
liver, kidney
Glucose
Glycogen
137
138
139
140
Phosphatase
Blood
Glucose
PO4
H2O
Glucose
Kinase
G6P
Ribose 5-PO4
Glycogen
F6P
Kinase
F1,6bisP
PO4
Phosphatase
H2O
Gly-3-P
DHAP
1,3 bisPGA
Kinase
3PGA
2PGA
PEP
Kinase
L-lactate
Pyruvate
OAA
141
3 irreversible reactions
PEP
F-6-PO4
Glucose
Pyruvate
F1,6-bisPO4
Glucose-6-PO4
Go’ = -61.9 kJ per mol
Go’= -17.2 kJ per mol
Go’= -20.9 kJ per mol
Take home: Gluconeogenesis feature enzymes
that bypass 3 irreversible KINASE steps
142
Reaction1
Glucose-6Phosphate
Glucose
Hexokinase
143
Reaction 3
Fructose-6Phosphate
Fructose-1,6Phosphate
Phosphofructokinase
144
Reaction 10:
Phosphoenolpyruvate
Pyruvate
145
3 reactions need to bypass:
Pruvate
Fructose 1,6-bisphosphate
Glucose 6-phosphate
phosphoenolpyruvate
fructose 6-phosphate
glucose
146
The conversion of pyruvate to
phosphoenolpyruvate(PEP)
mitochondria
CO2
Pyruvate
oxaloacetate
Pyruvate carboxylase
147
malate
oxaloacetate
aspartate
cytosol
PEP
oxaloacetate
malate
mitochondria
aspartate
148
GTP
GDP
oxaloacetate
Mitochondria or cytosol
PEP
CO2
Phosphoenolpyruvate carboxykinase
149
The conversion of Fructose 1,6-bisphosphate to
Fructose 6-phosphate
Fructose 1,6bisphosphate
Fructose 6-phosphate
Fructose 1,6-bisphosphatase
150
The conversion of glucose 6-phosphate to Glucose
glucose 6-phosphate
Glucose
Glucose 6-phosphatase
151
Substrate cycle
The interconversion of two substrates
catalyzed by different enzymes for singly
direction reactions is called substrate cycle.
Glucose
glucose-6-phosphote
152
153
Significance:
Primarily in the liver (80%); kidney (20%)
Maintains blood glucose levels
The anabolic arm of the Cori cycle
154
Cori Cycle
155
Cori cycle is a pathway in carbohydrate metabolism
that links the anaerobic glycolysis in muscle tissue to
gluconeogenesis in liver.
156
Liver is a major anabolic organ
L-lactate
Blood
Lactate
D-glucose
THE CORI CYCLE
L-lactate
Blood
Glucose
D-glucose
Muscle is a major catabolic tissue
157
Significance of cori cycle:
•avoid the loss of lactate and accumulation of
lactate in blood to low blood pH and acidosis.
•6 ATP are sonsumed per 2 lactate to glucose
158
Regulation of gluconeogenesis
There are 2 important regulatory points:
Fructose 1,6bisphosphate
Fructose 6-phosphate + Pi
Fructose 1,6-bisphosphatase
159
Fructose 1,6-bisphosphatase
Inhibitor:
Fructose 2,6-bisphosphate and AMP
Activitor:
Citrate
160
161
To summarize, when the concentration of glucose in
the cell is high, the concentration of fructose 2,6bisphosphate is elevated. This leads to a stimulation of
glycolysis .
Conversely, when the concentration of glucose is low,
the concentration of fructose 2,6-bisphosphate is
decreased. This leads to a stimulation of gluconeogenesis.
Gluconeogenesis predominates under starvation
conditions.
162
Pyruvate + CO2 +
ATP + H2O
.
oxaloacetate + ADP + Pi
+ 2 H+
pyruvate carboxylase
Pyruvate carboxylase is allosterically activated
by acetyl CoA
163
The Significance of
Gluconeogenesis


Replenishment of glucose and maintaining
normal blood sugar level
Replenishment of liver glycogen
“three carbon” compounds


Regulation of Acid-Base Balance
Clearing the products
lactate, glycerol

Glucogenic amino acids to glucose
164
Blood Sugar and Its Regulation

Blood sugar level
3.89-6.11mmol/l

Sources of blood sugar---income
digestion and absorption of glucose from dietary
gluconeogenesis
glycogen
other saccharides
Outcome:
aerobic oxidation
Glycogen
PPP
Lipids and amino acids
165
Regulation of Blood Glucose
Concentration

Insulin
decreasing blood sugar levels

Glucagon, epinephrine glucocorticoid
increasing blood sugar levels
166
Insulin
The unique
hormone responsible
for decreasing blood
sugar level and
promoting glycogen
formation, fat, and
proteins
simultaneously.
167
168
169
The effects of insulin:
Effects on membrane actively transport.
Effects on glucose utilization
Effects on gluconeogenesis.
170
Glucagon
171
Epinephrine
Stimulates glucogen degradation and gluconeogenesis
172
Glucocorticoids
Inhibit the utilization of glucose
Stimulate gluconeogenesis by stimulating protein
degradation to liberate amino acids
173
Review questions
174
Glucagon
175
•Epinephrine
•glucocorticoids
176