Transcript Fatty acids with

AV. Lipid metabolism 1-2. 2011
Fatty acid oxidation
Ketone bodies
Fatty acid synthesis
Triacylglycerols
Major energy reserve
Oxidation: 9 kcal/g
(for carbohydrates: 4 kcal/g)
11 kg of 70 kg total body weight
Site of accumulation: cytoplasm
of ADIPOSE CELLS
Adipose tissue
-specialized for synthesis,
storage, mobilization of lipids
Lipases
The most important fatty acids
Number of
carbons
Number of
double
bonds
Name
16
0
Palmitate
18
0
Stearate
20
0
Arachidate
16
1
Palmitoleate
Cis D9
18
1
Oleate
Cis D9
18
2
Linoleate
Cis D9, D12
18
3
Linolenate
Cis D9, D12, D15
20
4
Arachidonate Cis D5, D8, D11, D14
Mobilization of triacylglycerols stored in adipose tissue
Glukagon, adrenalin, ACTH
↓
receptor activation
↓
protein kinase A
↓
phosphorylation of Perilipin
(when dephosphorylated it inhibits the
access of lipases to TG and DG
+
phosphorylation of HSL
(hormon-sensitive lipase)
activation
↓
CGI dissociates from Perilipin
then associates with ATGL (adipocyte
trigliceride lipase)
↓
TG→DG + fatty acid
↓
HSL: DG→MG + fatty acid
↓
MGL (monoacylglycerol lipase):
MG→G + fatty acid
Lehninger, Principals of Biochemistry, 2013
ADIPOSE TISSUE
TG
CIRCULATION
Fatty acids
Fatty acids - bound to albumin
(10 fatty acids/albumin monomer)
(free fatty acids, FFA)
MUSCLE, HEART MUSCLE, RENAL CORTEX
Fatty acid activation, transport into the mitochondria, β-oxidation
Site of β-oxidation: mitochondria
Activation of fatty acids:
Fatty acid + ATP + CoA <------> Acyl-CoA + PPi + AMP
Acyl-CoA synthetase
O
1.
R-COOH
+
ATP
R
C AMP
+
PPi
O O
R
C
P
O Ribose
Adenin
O
acyl-adenylate
O
O
2.
R
C AMP
+
HS-CoA
R
C
S
CoA + AMP
acyl-CoA
Fast PPi hydrolysis
reaction is irreversible in vivo
Site of fatty acid activation:
cytosolic side of the mitochondrial outer membrane
Triacylglycerols
Major energy reserve
Oxidation: 9 kcal/g
(for carbohydrates: 4 kcal/g)
11 kg of 70 kg total body weight
Site of accumulation: cytoplasm
of ADIPOSE CELLS
Adipose tissue
-specialized for synthesis,
storage, mobilization of lipids
Lipases
The most important fatty acids
Number of
carbons
Number of
double
bonds
Name
16
0
Palmitate
18
0
Stearate
20
0
Arachidate
16
1
Palmitoleate
Cis D9
18
1
Oleate
Cis D9
18
2
Linoleate
Cis D9, D12
18
3
Linolenate
Cis D9, D12, D15
20
4
Arachidonate Cis D5, D8, D11, D14
Mobilization of fatty acids from the adipose tissue
Glukagon, adrenalin, ACTH
Receptor activation
Protein kináz A
Phosphorylation of Perilipin
(when dephosphorylated it inhibits the
access of lipase to TG,
phosphorylated perilipin has no such
effect)
+
Phosphorylation of Hormon-sensitive
lipase
(activation)
Mobilization of fatty acids from TG
Lipid droplet
ADIPOSE TISSUE
TG
CIRCULATION
Fatty acids
Fatty acids - bound to albumin
(10 fatty acids/albumin monomer)
(free fatty acids, FFA)
MUSCLE, HEART MUSCLE, RENAL CORTEX
Fatty acid activation, transport into the mitochondria, β-oxidation
Site of β-oxidation: mitochondria
Activation of fatty acids:
Fatty acid + ATP + CoA <------> Acyl-CoA + PPi + AMP
Acyl-CoA synthetase
O
1.
R-COOH
+
ATP
R
C AMP
+
PPi
O O
R
C
P
O Ribose
Adenin
O
acyl-adenylate
O
O
2.
R
C AMP
+
HS-CoA
R
C
S
CoA + AMP
acyl-CoA
Fast PPi hydrolysis
reaction is irreversible in vivo
Site of fatty acid activation:
cytosolic side of the mitochondrial outer membrane
Transport of fatty acids into the mitochondria
Transport of Long-chain (12-18 C atom) fatty acids with carnitine
Transport of fatty acids into the mitochondria
carnitine-acyltransferase I (CPT I)
Transport of carnitine-acylcarnitine is
the rate-limiting step and most
important control point in fatty acid
oxidation
carnitine-acyltransferase II (CPT II)
Fatty acids with <12 C enter mitochondria
without carnitine and are activated in the
mitochondria
Three isoenzymes:
-long-chain fatty acids (C 12-18)
-medium chain fatty acids (MCAD, 4-14)
-short-chain fatty acids (4-8)
MCAD deficiency is relatively frequent
Specific for L-stereoisomere
β-oxidation of fatty acids
Oxidation of fatty acids with >12 C is carried
out by a multienzyme bound to the
mitochondrial inner membrane, in which the
last three enzymes are tightly associated
(trifunctional protein),
when the chain is < 12 C soluble enzymes in
the matrix continue the oxidation
Conversion of glycerol to glycolysis
intermediate – in the liver
glycerol kinase
Glycerol-P dehydrogenase
Regulation of fatty acid oxidation
hormones
(adrenaline, glucagon)
High energy state
NADH
Malonyl-CoA
Inhibiton of Perilipin
Activation of hormone-sensitive lipase
Inhibition of
Inhibition of carnitine
3-hydroxyacyl CoA
acyltransferase I
dehydrogenase
Acetyl-CoA
thiolase
Increased level of free fatty acids
Entry of fatty acids
into mitochondria is
inhibited
Oxidation
Inhibition of ß-oxidation
Oxidation
Long-term regulation:
PPAR (peroxisome proliferator/activated receptors)
nuclear receptor – transcription factors
PPARα – muscle, adipose tissue, liver
regulate the transcription of fatty acid transporters, CPT I és CPT II,
and acyl-CoA dehydrogenase
- energy need (fasting, between-meal periods)
PPARα activation
transcription of enzymes of fatty acid oxidation
- fetus - principal fuels for heart: glucose and lactate
-neonatal – fatty acid
Regulation of metabolic transition by PPARα
- sustained exercise – PPARα expression in muscles
The most common genetic defect in fatty acid oxidation
Acyl-CoA dehydrogenase deficiency
For the medium length acyl-CoA dehydrogenase
Prevalence:
1:40 – mutation in one of the chromosomes
1:10000 – two mutant copies – disease manifestation
symptoms in the first years
-hypoglycemia – with decreased ketone body formation (decreased
fatty acid oxidation and gluconeogenesis in the liver)
-accumulation of lipids in the liver
-vomiting, drowsiness
Therapy:
frequent carbohydrate-rich meals + carnitine supply
Deficiency of carnitine transport into the mitochondria
Long-chain fatty acid transport
Carnitine deficiency
-high-affinity plasma membrane transporter
(heart, kidney, muscle – but not liver)
muscle cramps – weakness – death
addition of carnitine
-secondary carnitine deficiency
due to deficiency on β-oxidation acyl-carnitine in the urine
Carnititne acyltransferase deficiency
most common - CPT II gene mutation – partial loss of enzyme activity
muscle weakness
when more serious – hypoglycemia with decreased ketone body formation
FORMATION OF KETONE BODIES
GLUCONEOGENESIS
FATTY ACID
GLUCOSE
ß-oxidation
PYRUVATE
ACETYL-CoA
ANAPLEROTIKUS REAKCIÓ
OXALOACETATE
Ketone bodies
CITRATE
Fatty acid oxidation + lack of oxaloacetate
fasting
untreated diabetes
Synthesis of ketone bodies in the liver
Ketone bodies as fuels
Oxidation of ketone bodies in the extrahepatic tissues
heart muscle
striatal muscle
kidney
brain
Ketone bodies can be regarded as a transport form of acetyl groups
Important sources of energy: heart muscle, renal cortex (preference to glucose,
1/3 of the energy)
brain - glucose is the major fuel but in starvation
and diabetes brain uses acetoacetate
Ketone bodies
Fasting
Diabetes
high level of ketone bodies in the blood
KETOSIS
Formation in the liver exceeds the use in the periphery.
Level of ketone bodies after an overnight fast: ~0.05 mM
2 days starvation: 2 mM (40-fold increase!)
40 days: 7 mM
Fatty acid synthesis - repeated cycles
– in each cycle the chain is extended by two carbons
– four steps in each cycle
Enzyme:
fatty acid synthase
Seven active site for different
reactions in separate domains of
a single large polypeptide
Fatty acid synthesis –Lipogenesisnot a reversal of degradation
SYNTHESIS
BREAKDOWN
Site
Cytosol
Mitochondrial matrix
Intermediates bound to
Acyl-carrier protein
CoA
Enzymes
Joined in a single
polypeptide chain (fatty
acid synthase)
Not associated
Reducing equivalents
NADPH
NAD, FAD
Units
Malonyl-CoA
Acetyl-CoA
3-hydroxyacyl-derivative
D-enantiomer
L-enantiomer
Fatty acid synthesis:
*Liver
*Adipose tissue
*Lactating mammary gland
Committed step in fatty acid synthesis:
formation of malonyl-CoA from acetylCoA
acetyl-CoA carboxylase
- prosthetic group: biotin
Acetyl-CoA carboxylase has three activities in a single polypeptide
Biotin – covalently bound
to Lys έ-amino group
1. transfer of carboxyl group to
biotin
ATP-dependent
move of activated CO2 from the
biotin carboxylase region to the
transcarboxylase active site
2. transfer of the activated carboxil
group from biotin to acetyl-CoA
Critical SH-groups carry the intermediates during the synthesis of fatty acids
Acyl carrier protein
β-ketoacyl-ACP synthase
CH2 SH
Condenzing enzyme - cys
SH group is the site of ently of malonyl group
during fatty acid synthesis
SH
Fatty acid synthase
Acetyl group from Acetyl-CoA is
transferred to
Cys-SH of β-ketoacyl-ACP synthase (KS)
by MAT
Malonyl group is transferred to
ACP-SH by MAT
Acetyl group (from AcetylCoA) is transferred to the
malonyl group on ACP
(methyl terminal)
Acetoacetyl-ACP
Reduction
by β-ketoacyl-ACP reductase
Dehydration
by β-hydroxyacyl-ACP dehydratase
Reduction
by enoyl-ACP reductase
Second round of fatty acid synthesis cycle
ACP is recharged with another malonyl
group by MAT
The overall process of palmitate synthesis
Seven cycles for the synthesis of palmitate
Palmitate is released from ACP by thioesterase (TE)
STOICHIOMETRY
Seven cycles for the synthesis of palmitate
Ac-CoA + 7 malonyl-CoA + 14 NADPH + H+ 
Palmitate + 7 CO2 + 14 NADP+ + 8 CoA + 6 H2O
7 Ac-CoA + 7 CO2 + 7 ATP 7 malonyl-CoA + 7 ADP + 7 Pi
Overall:
8 Ac-CoA + 7 ATP + 14 NADPH + H+ 
palmitate + 14 NADP+ + 8 CoA + 6 H2O + 7 ADP + 7 Pi
Fatty acid synthase is present exclusively in the cytosol
In adipocytes and hepatocytes
cytosolic [NADPH]/[NADP] ratio is high (~75) – strongly reducing
environment
In hepatocytes and lactating mammary gland cytosolic NADPH is
generated largely by pentose phosphate pathway but malic enzyme is also
significant
MITOCHONDRION
CYTOSOL
Citrate carries Acetyl-CoA from
AcCoA
CITRATE
ATP:citrate lyase
CITRATE
AcCoA
OXALOACETATE
OXALOACETATE
NADH
MALATE
malic enzyme
PYRUVATE
PYRUVATE
NADPH
mitochondria to the cytosol for
fatty acid synthesis
Source of NADPH for fatty acid synthesis
Regulation of fatty acid synthesis
-regulation of Acetyl-CoA carboxylase-negative feed-back
inhibition by
palmitate
- allosteric stimulation
by citrate
-regulation by
covalent modification
Dephosphorylated
form – active
-Polymerizes into
long filaments
insulin
Phosphorylation
inactivates the enzyme
Active dephosphorylated ACC
Control of fatty acid synthesis
Short term regulation
• Ac-CoA
• ATP
isocitrate dehydrogenase inhibited
citrate – stimulates Ac-CoA carboxylase
+carries the substrate (Ac-CoA)
(indicates that two-carbon units & ATP are available
for synthesis)
Control of fatty acid synthesis
Glucagon
cAMP
activation of protein kinases
phosphorylation of Ac-CoA carboxylase - switch off
Palmitoyl-CoA
*Inhibits Ac-CoA carboxylase
*Inhibits translocation of citrate from mitochondria to
cytosol
*Inhibits glucose 6-P dehydrogenase  NADPH 
Control of fatty acid synthesis
Long term regulation
– low fat, high carbohydrate diet
the amount of Acetyl-CoA carboxylase & fatty acid synthase is
increased
- fasting and high fat diet
the amount of Acetyl-CoA carboxylase is decreased
High-fat low carbohydrate diet – Atkins diet
fatty acid mobilization - ketone body formation (loss in the urine)