Post on 05-Jan-2016
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Metabolic functions of liver
Seminar No. 7
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Compartment Metabolic pathways
Mitochondrion
Lysosome
Nucleus
Cytoplasm
Smooth ER
Rough ER
Golgi app.
3
Mitochondria β-oxidation FA, oxid. decarb. of pyruvate, CAC, resp. chain, AST reaction, synthesis of urea / KB / heme / glutamine
Lysosome nonspecific hydrolytic degradation of various substrates
Nucleus DNA replication, RNA synthesis = transcription
Cytoplasm glucose metabolism, ALT reaction, ethanol oxidation,
Synthesis of FA / urea / uric acid / heme
Smooth ERSynthesis of cholesterol / PL /TAG FA desaturation, biotransformation of xenobiotics (hydroxylation)
Rough ER proteosynthesis
Golgi app. protein glycosylation, sorting + export of proteins
4
Process Enzyme(s)
ALT, AST
succinate DH, malate DH
LD
carbamoyl-P-synthetase, arginase
glutaminase
GSH peroxidase ...
HMG-CoA reductase
Glc 6-phosphatase, PEPCK
Glycogen synthase
Periportal hepatocytes
5
Process Enzyme(s)
transamination ALT, AST
CAC succinate DH, malate DH
Gluconeogenesis (Cori cycle) LD
Urea synthesis carbamoyl-P-synthetase, arginase
Release of ammonia glutaminase
ROS elimination (reduction) GSH peroxidase ...
Cholesterol synthesis HMG-CoA reductase
gluconeogenesis Glc 6-phosphatase, PEPCK
Glycogen synthesis Glycogen synthase
Periportal hepatocytes
6
Process Enzyme(s)
GMD
Acetyl-CoA carboxylase
AD
Cytochromes P-450
Glutamine synthetase
UDP-glucuronyl transferase
glukokinase
Perivenous hepatocytes
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Process Enzyme(s)
Dehydrogenation deamination of Glu GMD
FA synthesis Acetyl-CoA carboxylase
Ethanol catabolism AD
hydroxylations Cytochromes P-450
Ammonia detoxication Glutamine synthetase
Conjugation reactions UDP-glucuronyl transferase
glycolysis glukokinase
Perivenous hepatocytes
8
Q. 2
9
A. 2
A) after meal: insulin decreases blood glucose by
stimulating liver glycolysis and synthesis of glycogen
B) in fasting: glucagon stimulates glycogenolysis and
gluconeogenesis
C) in starvation: glucagon stimulates gluconeogenesis
(liver glycogen is depleted)
10
Q. 3
11
A. 3
fructose and galactose are converted to glucose
What are dietary sources
of fructose and
galactose?
12
Q. 5
Glycolysis intermediate Non-hexose product
Glc-6-P
Fructose-6-P
DHAP
3-phosphoglycerate
13
A. 5
Glycolysis intermediate Non-hexose product
Glc-6-P Ribose (from pentose cycle)
Fructose-6-P Glucosamine glycosaminoglycans
DHAP Glycerol-3-P TAG
3-phosphoglycerate serine
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Synthesis of serine from glucose
3-P-glycerát
COOH
CHH2N
CH2OH
2-oxoglutarátGlu
COOH
C
CH2OH
O
serin hydroxypyruvát
NADH + H+COOH
CH
CH2OH
OH
glycerát
ATP
ADP
COOH
CH
CH2
OH
O P
O
O
O
glukosa
H2O
glycolysisglucose 3-P-glycerate
glycerate hydroxypyruvate serine
all reactions
are reversible
15
Q. 6
16
Asn
GlcNAc
GlcNAc
Man
Man
Man
GlcNAc GlcNAc
GlcNAc
GlcNAc
Gal Gal Gal Gal
Sial Sial Sial Sial
• Plasma (glyco)proteins and peptide
hormons (e.g. insulin) are taken up and
degraded in liver lyzosomes
• Glycoproteins lost sialic residues by the
action of neuramidase = terminal
galactose is the signal for
asialoglycoprotein receptor in liver
A. 6 (Harper, p. 526)
17
Q. 7
18
A. 7
• Liver produces most plasma proteins including coagulation
factors
• Severe liver damage = limited / no synthesis
• Deficit of coag. factors = increased bleeding
• Deficit of albumin (main plasma prot.) = oedemas
19
Q. 10
20
A. 10
• α1-antitrypsin is antiprotease
• Inhibits proteases produced by tissue and plasma cells
(trypsin, elastase, and other)
• Decreased production of α1-antitrypsin active proteases in
ECF tissue proteolysis tissue damages (emphysema,
liver diseases)
21
Q. 12
22
A. 12 Complete the names of compounds
H2C COOH
NH2
H2C COOH
NHCH2N
NH
H2C COOH
NCH2N
NH
CH3
H2C COOH
NCNH
NH
CH3P
O
O
O
............................
...
...............................................
.
.............................
from ......
from ..............
............................
...
kidneyliver
23
A. 12
H2C COOH
NH2
H2C COOH
NHCH2N
NH
H2C COOH
NCH2N
NH
CH3
H2C COOH
NCNH
NH
CH3P
O
O
O
glycine
guanidineacetate
creatine N-methylguanidine-N-acetic ac.
creatine phosphate
from Arg
from methionine
24
Q. 13
25
1. Low-protein diet
2. Alteration of colon microflora
• Probiotics – live bacteria supporting fermentation processes in
large intestine (lactobacillus, bifidobacteria)
• Prebiotics – nondigestible oligosaccharides – substrates for the
growth of probiotics (lactulose, oligofructose, inulin)
• Local intestinal antibiotics (neomycin, metronidazol) – kill all
intestinal microflora
To decrease NH3 formation in colon and its
concentration in portal blood – to protect liver A.13
26
Q. 14
27
A. 14
Dietary FA to liver:
• Short chain FA (< 12C) directly from portal blood (protein
transporter, cotransport with Na+)
• Other FA in CM remnants (apo E receptors)
• FA are oxidized to acetyl-CoA and CAC - energy
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Q. 15
29
A. 15
A) Synthesis of VLDL, HDL
B) Degradation - CM remnants, IDL, LDL, HDL2
(hepatic lipase, lysosome)
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A. 16
31
A. 16
• Saccharides are necessary for CAC
• The lack of saccharides = the excess of acetyl-CoA from
FA β-oxidation = synthesis of KB
• for export only
succinyl-CoA:acetoacetate-CoA transferase (for activation
of acetoacetate) is not expressed in liver
32
Q. 17
33
A. 17
• excretion of cholesterol into bile
• synthesis + conjugation of bile acids
• excretion of bile acids into bile
34
A. 18
35
7-HydroxycholesterolCholesterol
cytP450
O2 NADPH+H+OH
The first step is 7α-hydroxylation of cholesterol
3β
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7α-Hydroxycholesterol
5β-Cholestane-3α,7α,12α-triol
Cholate
Choloyl-CoA
Coenzyme A, ATP
Propionyl-CoA, ADP
Coenzyme A, ATP
ADP
MITOCHONDRION
26-HydroxylationOxidation to C-26 carboxylActivation to acyl-CoAPropionyl-CoA released
ER
Dehydrogenation to 3-oxo-Isomerization of the double bondHydrogenation of 3-oxo and double bond at C-4
O2 + NADPH+H+
Cyt P 450
amide linkage with
glycine or taurine
– conjugated bile acids
37
Bile acids are anionic surfactants
all polar groups are oriented on one side of molecule
38
Q. 22
39
A. 22
• Phospholipids
• Bile acids (salts)
• Cholesterol
• Bilirubin – responsible for colour
make a special ternary
micellar system
40
Q. 23
41
A. 23
Feature Insulin Glucagon
Formation in beta-cells, pancreas alfa-cells, pancreas
No. of AA / chains 51 / 2 29 / 1
Precursor (pre)proinsulin proglucagon
Plasma half-life 3 min 5 min
Inactivation in liver, (kidneys) liver
42
Q. 24
O CH2CHCOOH
NH2I
I
HO I
I
thyroxine
43
A. 24
• Inactivated
• Deiodination, deamination, decarboxylation
• conjugation with glucuronic acid
• conjugation with PAPS (sulfatation)
• More polar derivatives are excreted by urine
44
Q. 26
45
7-Dehydrocholesterol
Cholesterol
An intermediate(praevitamin)
Calciol (vit. D3)
LIVER 7,8-Dehydrogenation
SKIN photolysis
Slow thermal conversion
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C-25
1αThe LIVER CELLS
25-Hydroxylation(monooxygenase, cyt P450)
The RENAL TUBULAR CELLS
1α-Hydroxylation(monooxygenase, cyt P450)
Calciol(Cholecalciferol)
Calcidiol(25-Hydroxycholecalciferol)
Calcitriol(1α,25-Dihydroxycholecalciferol)
A CALCIOTROPIC STEROID HORMONE
47
Q. 27
48
A. 27
• Vitamin A (retinol)
• Vitamin B12 (cyanocobalamin)
Which reactions in the body require vitamin B12 ?
49
HOOC CH
NH2
CH2CH2 S
CH3
ATP
HOOC CH
NH2
CH2CH2 S
CH3
Rib Ad
HOOC CH
NH2
CH2CH2 SRib Ad
methionin
S-adenosylmethionin
S-adenosylhomocystein
HOOC CH
NH2
CH2CH2 SH
homocystein
remethylace
CH3 FH4
FH4
substrát
substrát CH3
cholinadrenalinkreatin
PPi + P i
B12
ethanolaminnoradrenalinguanidinacetát
substrate
Substrate-CH3
ethanolamine
noradrenaline
guanidineacetate
choline
adrenaline
creatine
remethylation
Remethylation of homocystein to methionine
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Production of succinyl-CoA from some AA
CH3 CH2 CS
O
CoA
CH3 CH CS
O
CoA
CHOO
CH2 CH2 CS
O
CoAHOOC
biotincarboxylation
B12isomeration
catabolism of
isoleucine
valine
methionine
?
............................ ............................
(complete the names)
51
Catabolism of hem
Metabolism of bilirubin
What is hem?
52
Hem is a chelate of protoporphyrin IX with Fe2+
protoporfyrin IX
Fe
hem
HN N
NNCH3H3C
CH3
H3C
COOHHOOC
H
askorbát
Fe3+
- 2H+N N
NNCH3H3C
CH3
H3C
COOHHOOC
Fe2+
ascorbic acid
AB
C D
53
Q. 31
54
A. 31 - Catabolism of hem
• occurs mainly in spleen, liver, bone marrow
• hemoxygenase (O2, NADPH, cytochrome P-450)
• Fe2+ is released and oxidized to Fe3+, bound to ferritin (store)
• -CH= between A/B rings is split off as carbon monoxide (CO)
• two O atoms are attached to the A+B pyrrole rings biliverdin
• the central -C= bridge between C/D rings in biliverdin is then
reduced to -CH2- bridge bilirubin
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A. 31 - Three oxygen atoms attack protoporphyrin
N HN
NNH
AB
OOO
one O is incorporated into CO, two O atoms are inserted into biliverdin
hemoxygenase
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A. 31 Hem degradation provides CO and bilirubin
N HN
NNH
oxidative splitting
CO + biliverdin + 3 H2O
bilirubin
3 O2 + 3 NADPH+H+
AB
what
happens
with CO?
57
Carbonylhemoglobin (CO-Hb) in blood
Subject / Situation CO-Hb (%)*
Newborns
Adults (rural areas)
Adults (big cities)
Smokers
Traffic policemen
Poisoning
Death
0.4
1-2
4-5
10-12
12-15
20-50
55-60
Endogenous CO
Exogenous CO
* Percentage of total hemoglobin
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Conjugation of bilirubin in liver
• bilirubin reacts with two molecules of UDP-glucuronate
• two highly polar molecules of glucuronate are attached to
bilirubin with glycosidic ester bond bilirubin bisglucuronide
• conjugated bilirubin is soluble in water (bile, plasma, urine)
• conj. bilirubin is excreted with bile into intestine, where it is
deconjugated and hydrogenated by microflora urobilinogens,
they are partially absorbed by v. portae and taken up by liver
59
The structure of UDP-glucuronate
N
OHOH
O
NH
O
O
OP
O
O
O
PO
O
OO
OH
O
COO
HH
N-glycosidic bondO-glycosidic bond
of ester type
60
Biosynthesis of UDP-glucuronate
O
OHOH
OH
O
CH2OP
H
O
OOH
OH
O
CH2HO
PH
O
OOH
OH
O
CH2HO
UDPH
UTP
glukosa-6-P glukosa-1-P UDP-glukosa
H
O
OOH
OH
O
C
UDP
OO NAD+
H2ONAD
+
glukosiduronáty
UDP-glukuronát
glucose-6-P glucose-1-P UDP-glucose
UDP-glucuronate
glucuronides
61
bilirubin bisglucuronide
62
Q. 34
63
A. 34 Hemoproteins
Protein Redox state Function
Hemoglobin
Myoglobin
Catalase
Peroxidase
Cytochromes
Cytochrome P-450
Fe2+
Fe2+
Fe3+
Fe3+
Fe2+ Fe3+
Fe2+ Fe3+
64
A. 34 Hemoproteins
Protein Redox state Function
Hemoglobin
Myoglobin
Catalase
Peroxidase
Cytochromes
Cytochrome P-450
Fe2+
Fe2+
Fe3+
Fe3+
Fe2+ Fe3+
Fe2+ Fe3+
transport of O2 in blood
deposit of O2 in muscle
elimination of H2O2
elimination of peroxides
resp. chain components
hydroxylation reactions
65
Q. 35
66
A. 35 Textbook structure of bilirubin
N
CH2 CH3
CH2
COOH
N
CH3
O
CH2
NO
H2C
H3C
N
CH3 CH2
CH2
CHOO
H H H H
bilirubinbilirubin has eight polar groups:
2 -COOH 2 C=O 4 -NH-
despite it bilirubine is non-polar compound
67
A. 35 Properties of bilirubin
• linear tetrapyrrol system
• free rotation around central -CH2- is possible
• non-linear conformation arises, stabilized by six
intramolecular H-bonds
• all polar groups are involved in H-bonds
• consequence: free bilirubin is non-polar, insoluble in
water, in plasma – bound to albumin
68
A. 35 Real structure of bilirubin
with six intramolecular H-
bonds
NO NH
H
C
O
OH
NNC
O
OH
HH O
69
Q. 36, 37
70
A. 36, 37
IcterusS-Bilirubin
unconjug.
S-Bilirubin
conjug.
U-Bilirubin
conjug.U-Ubg
Hemolytic ↑↑ - - ↑
Hepatic ↑↑ ↑ ↑ ↑↑
Obstructive normal ↑↑ ↑ -
Normal concentration of S-bilirubin
total bilirubine: 5-20 μmol/l
unconjugated up to: 12 μmol/l
conjugated up to: 5 μmol/l
See Lab manual
p. 60
S - serum, U - urine
71
Q. 38
72
A. 38
• Urobilinogens are resorbed from intestine to portal blood
• At hepatocellular disorders, the liver is incapable to take
urobilinogens, they become elevated in blood and thus
excreted to urine
73
Next seminar: 2nd Revision test
(15 Q / 20 min)
• Seminar chapters 4 – 7
• Practical chapters 3 – 5