1. Synthesis and degradation of fatty acids
Martina Srbová

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)
C14 – 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
acyl-CoA and glycerol-3-phosphate
synthesis of TAG in liver
stored mainly in adipose tissue
TAG transport from the liver to other tissues via VLDL
(especially skeletal muscle, adipose tissue)

5. 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

6. 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)

7. Precursors for FA biosynthesis
Acetyl-CoA +
HSCoA
OAA - oxaloacetate

8. FA biosynthesis
Formation of malonyl-CoA catalysed by acetyl-CoA-carboxylase (ACC)
HCO3- + ATP
ADP + Pi
enzyme-biotin
enzyme-biotin-COO- 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

9. FA biosynthesis on the multienzyme complex – FA synthase
repeated extension of FA by two carbons in each cycle
to the chain length C16 (palmitate)
ACP – acyl carrier protein

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

11. 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)

12. 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

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

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

15. 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

16. 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

17. FA biosynthesis FA desaturation
in the endoplasmic reticulum
4 desaturases:
double bonds at position  4,5,6,9
linoleic, linolenic – essential FA
enzymes: desaturase, NADH-cyt b5-reductase
process requiring O2, NADH, cytochrome b5
stearoyl-CoA + NADH + H+ + O oleoyl-CoA + NAD+ + 2H2O

18. FA biosynthesis - summary
Formation of malonyl-CoA
Acetyl-CoA-carboxylase
FA synthesis
Palmitic acid
FA Synthase– cytosol
Saturated fatty acids(>C16)
Elongation systems- mitochondria, ER
Unsaturated fatty acids
Desaturation system - ER -

19. FA degradation function: major energy source 1 2 3 4 5
(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 1
entry of FA into target cells 2
activation to acyl-CoA
transfer of acyl-CoA via carnitine system into mitochondria 3 4
β-oxidation 5
In the liver , acetyl CoA is converted to ketone bodies

20. FA degradation β-carbon -carbon -carbon -oxidation β-oxidation
C10 , C12
Branched FA
VLCFA

21. FA degradation β-oxidation localization: enzymes: substrate:
mainly in muscles
localization:
mitochondrial matrix
peroxisome (VLCFA)
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

22. 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

23. 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

24. FA degradation Substrate specifity for: SCFA MCFA LCFA VLCFA
acyl CoA synthetase
Substrate specifity for:
SCFA
MCFA
LCFA
VLCFA
Localization
Outer mitochondrial membrane ER
SCFA, MCFA
Mitochondrial matrix

25. FA degradation
The role of carnitine in the transport of LCFA 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

26. FA degradation Carnitine 3-hydroxy-4-N-trimethylaminobutyrate Sources:
Exogenous: meat, dairy products
Endogenous: synthesis from lysine and methionine
Transported into the cell by specific transporter
Deficiency:
Decreased transport of acyl-CoA into mitochondria
lipids accumulation
myocardial damage
muscle weakness
Increased utilization of Glc
hypoglycemia
Similar symptoms are the genetically determined deficiency carnitinpalmitoyltransferase I or II

27. 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

28. FA degradation Oxidation of unsaturated FA
the most common unsaturated FA in the diet:
β-oxidation of oleic acids
oleic acid, linoleic acid
degradation of unsaturated FA
by β-oxidation to a double bond
3 rounds of β-oxidation
Unsaturated FA are cis isomers - aren´t substrate for enoyl-coA hydratase
conversion of cis-isomer of FA
by specific isomerase to trans-isomer
intramolecular transfer of double bond
from β- to - β position
continuation of β-oxidation
Normal intermediates of β-oxidation

29. 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
methylmalonyl-CoA
carboxylation of propionyl-CoA
methylmalonyl-CoA mutase
(B12)
intramolecular rearrangement to form succinyl-CoA
succinyl-CoA
entry of succinyl-CoA into the citric acid cycle

30. FA degradation Peroxisomal oxidation of VLCFA
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

31. FA degradation Peroxisomal oxidation of VLCFA
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
In peroxisome shortened FA bind to carnitine acylcarnitine
transfer acylcarnitine into mitochondrion β-oxidation

32. mixed function oxidase
FA degradation
- oxidation
Excreted in the urine
mixed function oxidase
Oxidation  carbon
ER liver, kidney
Substrates C10 a C12 FA
Products: dicarboxylic acids

33. Comparison of FA biosynthesis and FA degradation

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

35. Ketone bodies
Ketogenesis

36. 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

37. 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

38. 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

39. 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.