1

Metabolic functions of liver

Seminar No. 7

2

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

7

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

14

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

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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

28

Q. 15

29

A. 15

A) Synthesis of VLDL, HDL

B) Degradation - CM remnants, IDL, LDL, HDL2

(hepatic lipase, lysosome)

30

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

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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

50

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?

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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