1. Synthesis and degradation of fatty acids
Zdeňka Klusáčková

2. Fatty acids (FA) Groups of FA:
mostly an even number of carbon atoms and linear chain
in esterified form as component of lipids
in unesterified form in plasma
binding to albumin
Groups of FA:
according to the chain length
<C6
short-chain FA (SCFA)
C6 – C12
medium-chain FA (MCFA)
C12 – C20
long-chain FA (LCFA)
>C20
very-long-chain FA (VLCFA)
according to the number of double bonds
no double bond
saturated FA (SAFA)
one double bond
monounsaturated FA (MUFA)
more double bonds
polyunsaturated FA (PUFA)

3. Overview of FA

4. Triacylglycerols main storage form of FA
acylglycerols with three acyl groups
stored mainly in adipose tissue

5. FA biosynthesis function: energy storage in the form of TAG
FA biosynthesis in the excess of energy (increased caloric intake)
acyl-CoA and glycerol-3-phosphate
synthesis of TAG in liver
TAG incorporation into very low density lipoproteins (VLDL)
entry of VLDL into the blood circulation
TAG transport from the liver to other tissues via VLDL
(especially skeletal muscle, adipose tissue)

6. FA biosynthesis localization: enzymes: primary substrate:
mainly in the liver, adipose tissue, mammary gland during lactation
(always in excess calories)
localization:
cell cytoplasm (up to C16)
endoplasmic reticulum, mitochondrion
(elongation = chain extension)
enzymes:
acetyl-CoA-carboxylase (HCO3- - source of CO2, biotin, ATP)
fatty acid synthase (NADPH + H+, pantothenic acid)
primary substrate:
acetyl-CoA
final product:
palmitate

7. FA biosynthesis on the multienzyme complex – FA synthase
repeated extension of FA by two carbons in each cycle
to the chain length C16 (palmitate)
palmitate, a precursor of saturated and unsaturated FA:
saturated FA (> C16)
elongation systems
unsaturated FA
desaturation systems

8. Precursors for FA biosynthesis1.
Acetyl-CoA
source:
oxidative decarboxylation of pyruvate (the main source of glucose)
degradation of FA, ketones, ketogenic amino acids
transport across the inner mitochondrial membrane as citrate 2.
NADPH
source:
pentose phosphate pathway (the main source)
the conversion of malate to pyruvate
(NADP+-dependent malate dehydrogenase - „malic enzyme”)
the conversion of isocitrate to α-ketoglutarate
(isocitrate dehydrogenase)

9. FA biosynthesis Formation of malonyl-CoA HCO3- + ATP ADP + Pi
enzyme-biotin
enzyme-biotin-COO-
biotinyl-enzyme
carboxybiotinyl-enzyme 1
carboxylation of biotin 2
transfer of carboxyl group to acetyl-CoA
acetyl-CoA
formation of malonyl-CoA +
enzyme-biotin
enzyme – acetyl-CoA-carboxylase
malonyl-CoA

10. FA biosynthesis Regulation at the level of ACC glucagon adrenaline
cAMP
insulin
AMP
protein kinase A
AMP-dependent
protein kinase A
glucose
citrate
acetyl-CoA
malonyl-CoA
palmitate
palmitoyl-CoA
acetyl-CoA carboxylase

11. FA biosynthesis
FA synthase

12. FA biosynthesis The course of FA biosynthesis transacylation
acetyl-CoA
malonyl-CoA
CoASH
CoASH
acetyltransacylase
malonyltransacylase
transacylation
acyl(acetyl)-malonyl-
-enzyme complex

13. FA biosynthesis The course of FA biosynthesis condensation CO2
3-ketoacyl-synthase
CO2
condensation
acyl(acetyl)-malonyl-enzyme complex
3-ketoacyl-enzyme complex
(acetacetyl-enzyme complex)

14. FA biosynthesis The course of FA biosynthesis first reduction
NADPH + H+
NADP+
NADPH + H+
NADP+
H2O
3-ketoacyl-reductase
3-hydroxyacyl-
dehydrase
enoylreductase
first reduction
dehydration
second reduction
3-ketoacyl-enzyme complex
(acetoacetyl-enzyme complex)
3-hydroxyacyl-enzyme complex
2,3-unsaturated acyl-enzyme complex
acyl-enzyme complex

15. FA biosynthesis Repetition of the cycle malonyl-CoA
CoASH
acyl-enzyme complex
(palmitoyl-enzyme complex)

16. FA biosynthesis The release of palmitate + H2O palmitate
thioesterase +
H2O
palmitate
palmitoyl-enzyme complex

17. FA biosynthesis The fate of palmitate after FA biosynthesis
acylglycerols
cholesterol esters
ATP + CoA
AMP + PPi
esterification
palmitate
palmitoyl-CoA
acyl-CoA-synthetase
elongation
desaturation
acyl-CoA

18. FA biosynthesis FA elongation 1. microsomal elongation system
in the endoplasmic reticulum
malonyl-CoA – the donor of the C2 units
NADPH + H+ – the donor of the reducing equivalents
extension of saturated and unsaturated FA
FA > C16
elongases
(chain elongation)
palmitic acid (C16)
fatty acid synthase 2.
mitochondrial elongation system
in mitochondria
acetyl-CoA – the donor of the C2 unit
not reverse β-oxidation

19. FA biosynthesis Microsomal extension of FA Example: + + synthase
CoASH + CO2 +
synthase
acetyl-CoA
malonyl-CoA
3-ketoacyl-CoA
NADPH + H+
NADP+
H2O
NADPH + H+
NADP+
reductase
hydratase
reductase
3-hydroxyacyl-CoA
2,3-unsaturated acyl-CoA
acyl-CoA
Example:
CoASH + CO2 +
palmitoyl-CoA
malonyl-CoA
NADPH + H+
NADP+
NADPH + H+
NADP+
H2O
stearoyl-CoA

20. FA biosynthesis FA desaturation in the endoplasmic reticulum
process requiring O2, NADH, cytochrome b5

21. FA degradation function: major energy source
(especially between meals, at night, in increased demand for energy intake – exercise)
release of FA from triacylglycerols in adipose tissue into the bloodstream
binding of FA to albumin in the bloodstream
transport to tissues
entry of FA into target cells
activation to acyl-CoA
transfer of acyl-CoA via carnitine system into mitochondria
β-oxidation
Most important FA released from adipose tissue:
palmitic acid
oleic acid
stearic acid

22. FA degradation Mechanisms of FA degradation
long-chain FA (LCFA, C12 – C20)
mitochondrial β-oxidation
unsaturated FA
modified
odd-chain-length FA
mitochondrial β-oxidation
very-long-chain FA (VLCFA, > C20)
peroxisomal β-oxidation
long-chain branched-chain FA
peroxisomal α-oxidation
FA with C10 or C12
ω-oxidation

23. FA degradation β-oxidation ω-oxidation α-oxidation
Mechanisms of FA degradation
β-oxidation
ω-oxidation
α-oxidation

24. FA degradation β-oxidation localization: enzymes: substrate:
mainly in muscles
localization:
mitochondrial matrix
peroxisome
enzymes:
acyl CoA synthetase
carnitine palmitoyl transferase I, II; carnitine acylcarnitine translocase
dehydrogenase (FAD, NAD+), hydratase, thiolase
substrate:
acyl-CoA
final products:
acetyl-CoA
propionyl-CoA

25. FA degradation β-oxidation PRODUCTION OF LARGE QUANTITY OF ATP
repeated shortening of FA by two carbons in each cycle
cleavage of two carbon atoms in the form of acetyl-CoA
oxidation of acetyl-CoA to CO2 and H2O in the citric acid cycle
complete oxidation of FA
generation of 8 molecules of acetyl-CoA from 1 molecule of palmitoyl-CoA
production of NADH, FADH2
reoxidation in the respiratory chain to form ATP
PRODUCTION OF LARGE QUANTITY OF ATP

26. FA degradation Activation of FA fatty acid+ ATP + CoASH
acyl-CoA-synthetase
acyl adenylate
pyrophosphate (PPi)
acyl-CoA-synthetase
pyrophosphatase
2Pi
acyl-CoA
AMP
fatty acid+ ATP + CoASH
acyl-CoA + AMP + PPi
PPi + H2O
2Pi

27. FA degradation
The role of carnitine in the transport of FA into mitochondrion
FA transfer across the inner mitochondrial membrane
by carnitine and three enzymes:
carnitine palmitoyl transferase I (CPT I)
acyl transfer to carnitine
carnitine acylcarnitine translocase
acylcarnitine transfer across
the inner mitochondrial membrane
carnitine palmitoyl transferase II (CPT II)
acyl transfer from acylcarnitine back to CoA in the mitochondrial matrix

28. FA degradation β-oxidation Steps of cycle: acyl-CoA trans-Δ2-enoyl-CoA
dehydrogenation
oxidation by FAD
creation of unsaturated acid
acyl-CoA-dehydrogenase
trans-Δ2-enoyl-CoA
hydration
addition of water on the β-carbon atom
creation of β-hydroxyacid
enoyl-CoA-hydratase
L-β-hydroxyacyl-CoA
L-β-hydroxyacyl-CoA-
dehydrogenation
oxidation by NAD+
creation of β-oxoacid
-dehydrogenase
β-ketoacyl-CoA
cleavage at the presence of CoA
formation of acetyl-CoA
formation of acyl-CoA (two carbons shorter)
β-ketoacyl-CoA-thiolase
acyl-CoA
acetyl-CoA

29. FA degradation Oxidation of unsaturated FA
the most common unsaturated FA in the diet:
linoleoyl-CoA
oleic acid, linoleic acid
cis Δ9, cis-Δ12
3 rounds of β-oxidation
3 acetyl-CoA
degradation of unsaturated FA
by β-oxidation to a double bond
cis-Δ3, cis-Δ6
enoyl-CoA-isomerase
conversion of cis-isomer of FA
by specific isomerase to trans-isomer
trans-Δ2, cis-Δ6
continuation of β-oxidation
to the next double bond
β-oxidation
1 acetyl-CoA
cis-Δ4
acyl-CoA-dehydrogenase
formation of double bond between C2 and C3 by dehydrogenation
trans-Δ2, cis-Δ4
NADPH + H+
elimination of double bond between C4 and C5 by reduction
dienoyl-CoA-reductase
NADP+
trans-Δ3
enoyl-CoA-isomerase
intramolecular transfer of double bond
trans-Δ2
continuation of β-oxidation
4 rounds of β-oxidation
5 acetyl-CoA

30. FA degradation Oxidation of odd-chain FA shortening of FA to C5
propionyl-CoA
shortening of FA to C5
stopping of β-oxidation
HCO3- + ATP
propionyl-CoA carboxylase
(biotin)
ADP + Pi
formation of acetyl-CoA and propionyl-CoA
D-methylmalonyl-CoA
carboxylation of propionyl-CoA
methylmalonyl-CoA racemase
epimerization of D-form into L-form
L-methylmalonyl-CoA
intramolecular rearrangement to form succinyl-CoA
methylmalonyl-CoA mutase
(B12)
entry of succinyl-CoA into the citric acid cycle
succinyl-CoA

31. FA degradation Peroxisomal oxidation of FA
A) very-long-chain FA (VLCFA, > C20)
transport of acyl-CoA into the peroxisome without carnitine
Differences between β-oxidation in the mitochondrion and peroxisome:
1. step – dehydrogenation by FAD
mitochondrion: electrons from FADH2 are delivered to the respiratory chain
where they are transferred to O2 to form H2O and ATP
peroxisome: electrons from FADH2 are delivered to O2 to form H2O2, which is degraded by catalase to H2O and O2
3. step – dehydrogenation by NAD+
mitochondrion: reoxidation of NADH in the respiratory chain
peroxisome: reoxidation of NADH is not possible,
export to the cytosol or the mitochondrion

32. FA degradation Peroxisomal oxidation of FA
Differences between β-oxidation in the mitochondrion and peroxisome:
4. step – cleavage at the presence of CoA
acetyl-CoA
mitochondrion: metabolization in the citric acid cycle
peroxisome: export to the cytosol, to the mitochondrion (oxidation)
a precursor for the synthesis of cholesterol and bile acids
a precursor for the synthesis of fatty acids
of phospholipids

33. FA degradation Peroxisomal oxidation of FA
B) long-chain branched-chain FA
blocking of β-oxidation by the alcyl group at Cβ
α-oxidation
hydroxylation at Cα
cleavage of the original carboxyl group as CO2
methyl group is in the position α
shortening of FA to 8 carbons
transfer of FA in the form of acylcarnitine into the mitochondrion
complete of β-oxidation in the mitochondrion

34. Refsum's disease rare autosomal recessive hereditary disease
phytanic acid
a product of metabolism of phytol (part of chlorophyll)
in milk and animal fats
decreased activity of peroxisomal α-hydroxylase
accumulation of phytanic acid
(in tissues of nervous system and serum)
ataxia, night blindness, hearing loss, skin changes etc.

35. FA degradation ω-oxidation of FA minor pathway of FA oxidation
in the endoplasmatic reticulum
repeated oxidation of ω-carbon
-CH CH2OH COOH
formation of dicarboxylic acid
entry of dicarboxylic acid into β-oxidation
reduction of FA to adipic acid (C6) or suberic acid (C8)
excreted in the urine

36. FA degradation Regulation of β-oxidation acetyl-CoA malonyl-CoA CPT I
A) by energy demands of cell
by the level of ATP and NADH:
FA can not be oxidized faster than NADH and FADH2 are reoxidized in the respiratory chain
B) via carnitine palmitoyl transferase I (CPT I)
CPT I is inhibited by malonyl-CoA, which is generated in the synthesis of FA by acetyl-CoA carboxylase (ACC)
active FA synthesis
inhibition of β-oxidation
acetyl-CoA
malonyl-CoA
CPT I
β-oxidation
ACC

37. Comparison of FA biosynthesis and FA degradation

38. Ketone bodies Ketogenesis localization: substrate: products:
in the liver
localization:
mitochondrial matrix
substrate:
acetyl-CoA
products:
acetone
acetoacetate
D-β-hydroxybutyrate
conditions:
in excess of acetyl-CoA
function:
energy substrates for extrahepatic tissues

39. Ketone bodies
Ketogenesis

40. Ketone bodies Ketogenesis acetoacetate waste product (lung, urine)
spontaneous decarboxylation to acetone
conversion to D-β-hydroxybutyrate
by D-β-hydroxybutyrate dehydrogenase
waste product (lung, urine)
energy substrates
for extrahepatic tissues

41. Ketone bodies Utilization of ketone bodies
water-soluble FA equivalents
energy source for extrahepatic tissues
(especially heart and skeletal muscle)
in starvation - the main source of energy
for the brain
energy
citric acid cycle
production

42. Ketone bodies Production, utilization and excretion of ketone bodies
acetyl-CoA
oxidation in the citric acid cycle (liver)
conversion to ketone bodies
(liver - mitochondrion)
release of ketone bodies into blood
transport to tissues

43. Ketone bodies Ketogenesis increased ketogenesis: lipolysis
starvation
prolonged exercise
diabetes mellitus
FA in plasma
high-fat diet
low-carbohydrate diet
β-oxidation
utilization of ketone bodies as an energy source
(skeletal muscle, intestinal mucose, adipocytes, brain, heart etc.)
excess of acetyl-CoA
to spare of glucose and muscle proteins
ketogenesis

44. Bibliography and sources
Devlin, T. M. Textbook of biochemistry: with clinical correlations. 6th edition. Wiley-Liss, 2006.
Marks, A.; Lieberman, M. Marks' basic medical biochemistry: a clinical approach. 3rd edition. Lippincott Williams & Wilkins, 2009.
Matouš a kol. Základy lékařské chemie a biochemie. Galén, 2010.
Meisenberg, G.; Simmons, W. H. Principles of medical biochemistry. 2nd edition. Elsevier, 2006.
Murray et al. Harper's Biochemistry. 25th edition. Appleton & Lange, 2000.