de novo synthesis of fatty acids
DESCRIPTION
biochemTRANSCRIPT
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DE NOVO SYNTHESISOF
FATTY ACIDSFloro B. Madarcos, MDDept. of Biochemistry
URMMMC College of Medicine
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OBJECTIVES At the end of the lecture, the
student should be able to discuss de novo synthesis of fatty acids in terms of: Definition of the pathway Sites – organs and intracellular Reaction steps and regulation Role of fatty acid multienzyme
complex End product
Modifications and examples Sources of NADPH2
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DE NOVO SYNTHESIS OFFATTY ACIDS
I.Definition
The process of combining eight 2-carbonfragments (acetyl groups from acetyl CoA) fo form a 16-carbon saturated
fatty acid palmitate.
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DE NOVO SYNTHESIS OFFATTY ACIDS
II. Cellular Location
Cytoplasm
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DE NOVO SYNTHESIS OFFATTY ACIDS
III. Sites A. Main – liver and adipocytesB. Other Sites
Nervous system Special tissues under specific conditions, such as the mammary glands during lactation
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HCO3- + ATP
Citrate lyase
Pyruvate
OxaloacetatePi + ADP
Pyruvatecarboxylase
(biotin)Acetyl-CoA
HS-CoA + NAD
CO2 + NADPH
Pyruvatedehydrogenase
complex
CitrateHS-CoA
Mitochondrial Matrix
H+
CitrateAnion
(Malate, Pyruvate or Pi)
Cytosol
Malate
Oxaloacetate
NAD+
NADH + H+
Malatedehydrogenase
Acetyl CoA
HS-CoA
Pi + ADP
ATP
PyruvateMalic enzyme
NADPH2NADP
IV. REACTIONS OF DE NOVO SYNTHESIS OF FATTY ACIDS
First Step: Production of Cytosolic Acetyl CoA by the Citrate Transport System
Citrate synthase
Pt
To FA Synthesis
CO2
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IV. REACTIONS OF DE NOVO SYNTHESIS OF FATTY ACIDS
B. Second Step: Carboxylation of Acetyl CoA to Malonyl CoA
O ||CH3 – C – S – CoA
ACETYL CoA
ATP
ADP + Pi
O O \ || C – CH2 – C – S – CoA //O MALONYL CoA
Acetyl CoA carboxylase(Biotin)
HCO3-
(CO2)
CitrateInsulinHigh CHOLow FatHigh Prot. +
Malonyl CoAPalmitoyl CoAEpinephrineGlucagonHigh FatFasting
- H2O
Mn+2BiotinRegulation1. Short Term Covalent Allosteric2. Long Term
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V. FATTY ACID SYNTHASE MULTIENZYME COMPLEX
β-KETO-ACYL
SYNTHASE
ACETYLTRANS ACY-LASE
MALONYLTRANSACYLLASE
HYDRATASE ENOYL
REDUCTASEβ-KETOACYL
REDUCTASE
ACPTHIO
ESTERASE
THIOESTERASE
KETOACYL
REDUCTASE ENOYL REDUCTASE
HYDRATASE
MALONYLTRANSACYLLASE
ACETYLTRANS ACY-LASE
β-KETO-ACYL
SYNTHASE
4-PHOSPHO-PANTETHEINE
SH
CYS
SUBUNITDIVISION
FUNCTIONAL
UNIT
CYS
SH
SH
ACP
SH
4-PHOSPHO-PANTETHEINE
Pantothenic acid
1
2
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REACTIONS OF FATTY ACIDSYNTHASE
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CYS–SH
ACP–SH
O ||CH3 – C – S – CoA Acetyl CoA
1Acetyl CoA trans-
acylase
CYS–SH O ||ACP–S – C – CH3
Acetyl-S-ACP
0 ||CYS–S-C-CH3 ACP–SH2
0 ||CYS–S-C-CH3
O O || |ACP–S-C-CH2-C |
O O|| ||C-CH2-C-S-CoA|O
Malonyl CoA
3Malonyl trans
acylase Malonyl-S-ACP
CO2
CYS–SH O O || ||ACP–S – C – CH2 – C – CH3
Acetoacetyl – S - ACP
CYS–SH O || H OH ACP–S – C – C – C – CH3
H Hβ- KetohydroxyButyryl –S-ACP
4
5
NADPH+ + H+NADP+
β-KetoacylACP-synthase
β-KetoacylACP-reductase
CYS–SH O || ACP–S – C – CH = CH – CH3
Crotonyl – S - ACP
H2O
β- HydroxylACP-dehydratase
6
NADPH+ + H+
NADP+
7 Enoyl ACP-reductase
ACP– SH
ACP– S-C-CH2
O ||
CYS– S – C - CH2 – CH2 – CH3
O ||
CYS– S – C - CH2 – CH2 – CH3
O O || || C-CH2-C-S-CoA |O
Malonyl CoA
9
O||-C|
O
CYS–SH O || ACP–S – C – CH2 – CH2 – CH3
Butyryl–S-ACP4-Carbon Sat.
Fatty Acyl-ACP CYS–SH O O || ||ACP–S – C – CH2 – C – CH2 – CH2 - CH3
CO2
10
CYS–SH O || ACP–S – C – CH2 – CH2 – CH2 – CH2 - CH3
NADPH+ + H+NADP+NADP+
NADPH+ + H+ H2O
567
CYS–SHACP–S-Palmitate
CYS–SHACP–SHPalmitoyl
thioesteraseRepeat steps
(2) - (7)5x more
6-Carbon sat.Fatty Acyl-ACP 16-Carbon sat.
FA (Palmitoyl ACP) + Palmitate (C16)
VI. REACTIONS OF FATTY ACID SYNTHASE
Butyryl– S-ACP
8
O
CoA1 2
321
12
12 3
124 3
12
12
VI. SYNTHESIS OF PALMITATE (Lippincott’s Biochem, 4TH ed.)
FA synthase
124 36 5
12345
6
Keto group at β-
carbon
α
H2O
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STRUCTURE OF PALMITATE (16:0)
O
β α ||CH3–CH2–CH2–CH2–CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-C-O16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Carboxyl endMethyl end
Acetyl CoA
Malonyl CoA
(16 carbons; no double bond)
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VII. SOURCES OF NADPH2 FOR FATTY ACID
SYNTHESISPentose Phosphate Pathway
(HMP)Cytosolic conversion of malate to
pyruvateExtramitochondrial isocitrate
dehydrogenase - ruminants
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6 - Phosphogluconate dehydrogenase
NON-OXIDATIVE
STAGE
Glucose 6 – phosphate
6 – phosphogluconate
6 – phosphogluconolactone
Ribulose 5 – phosphate
Ribose 5 – phosphate Xylulose 5 – phosphate
Glyceraldehyde 3 – phosphate
Seduloheptulose 7– phosphate
Fructose 6 – phosphate
Erythrose 4 – phosphate
Fructose 6 – phosphate
Glyceraldehyde 3 – phosphate
GLYCOLYSIS
G6P dehydrogenase
Gluconolactone hydrolase
Transketolase
Transketolase
Transaldolase
OXIDATIVE STAGE
NAPD
NADPH + H
H2O
H+
NAPDNADPH + H
CO2
VIII. PENTOSE PHOSPHATE PATHWAY AS A SOURCE OF NADPH2
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HCO3- + ATP
Mitochondrial Matrix
Acetyl CoA
IX. CYTOSOLIC CONVERSION OF MALATE TO PYRUVATE AS A SOURCE OF NADPH2
Citrate lyase
Pyruvate
OxaloacetatePi + ADP
Pyruvatecarboxylase Acetyl-CoA
HS-CoA + NAD
CO2 + NADPH
Pyruvatedehydrogenase
complex
CitrateHS-CoA
H+
CitrateAnion
(Malate, Pyruvate or Pi)
Cytosol
Malate
Oxaloacetate
NAD+
NADH + H+
Malatedehydrogenase
HS-CoA
Pi + ADP
ATP
PyruvateMalate dehydrogenase
(malic enzyme)
NADPH2NADP+
Citrate synthase
Pt
To FA Synthesis
CO2
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O-
IC – C – CH2 - IIO
O-
IC IIO
OII
O-
IC – C – CH2 - IIO
O-
IC IIO
OH II
IH
O-
IC – C - IIO
OIIC ICH3
Cytosolic NADH-dependentmalate dehydrogenase
NADH + H+ NAD+
NADP+-dependentmalate dehydrogenase
(malic enzyme)
NADP+
NADPH + H+
CO2
Oxaloacetate
Pyruvate
Malate
CYTOSOLIC CONVERSION OF MALATE TO PYRUVATE AS A SOURCE OF NADPH2
Glyceraldehyde 3-PO4
dehydrogenase reaction(glcolysis)
Reductive synthesis
of FAs, steroids,
sterols
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X. BALANCE SHEET FOR THE CONVERSION OF ACETYL CoA
TO PALMITATE
8Acetyl CoA + 7Malonyl CoA + 14NADPH
+ 14H+
1Palmitate + 7CO2 + 8CoA + 14NADP+ + 6H2O
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XI. PAMITATE MODIFICATION
Chain Elongation Desaturation Hydroxylation
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XII. PAMITATE MODIFICATION
Sites ER – Malonyl CoA/ NADPH/
Palmitoyl CoA Mitochodrion – Acetyl CoA,
NAD & NADPH
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XIII. FATTY ACID CHAIN ELONGATION
IN THE ENDOPLASMIC RETICULUMPALMITOYL CoA
β-KETOACID
MALONYL CoA
REDUCTION(similar to de novo
pathway)
SATURATED FA 26 CARBONS (even numbers)
NADPH
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XIV. FATTY ACID ELONGATION IN THE MITOCHONDRION
O ||
R – CH2 – C – SCoA (Fatty acyl CoA)
O O | | ||R – CH2 – C – CH2 – C – SCoA
O ||CH3 – C – SCoA
CoASH β-ketothiolase
OH O | ||R – CH2 – CH – CH2 – C – SCoA
β-hydroxyacyl CoAdehydrogenase
NADH + H+
NAD+
O ||R – CH2 – CH = CH – C – SCoA
Enoyl CoAhydratase
H2O
O ||R – CH2 – CH2 – CH2 – C – SCoA
NADP+
NADPH + H+ Enoyl CoAreductase
Acetyl CoA
Fig. 17.12, p. 685, Devlin’s Textbook of Biochemistry, 7th ed.
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XV. FATTY ACID DESATURATION
SAT. FATTY ACID
UNSAT. FATTY ACID(monoenoic fatty acid)
Cytochrome b5
NADPH-cytochrome b5 reductase
O2 Δ9
UNSAT. FATTY ACID
UNSAT. FATTY ACID(with more = bonds)
Δ4Δ5Δ6
Fatty acid desaturase
Cytochrome b5
NADPH-cytochrome b5 reductase
O2
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XVI. FATTY ACID DESATURATION- EXAMPLES
16:0 (Sat. FA Palmitic acid)
18:0 (Sat. FAStearic acid )
18:2Δ9,12
(Dienoic FA)
16:Δ9 (Unsat. FAPalmitoleic acid)
18:3Δ6,9,12
(Trienoic FA)18:1Δ9 (Unsat. FA
Oleic acid)
Δ9(Stearoyl-CoAdesaturase)
Δ6
ω-7 ω-6ω-9
A B C
Δ9(Stearoyl-CoAdesaturase)
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XVII. EXAMPLE OF FATTY ACID DESATURATION
O ||
CH3–CH2–CH2–CH2–CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-C-O16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
O
||
CH3–CH2–CH2–CH2–CH2-CH2-CH = CH- CH2-CH2-CH2-CH2-CH2-CH2-CH2-C-O16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Palmitate (C16:0); saturatedO2
2 H2O
∆9 desaturase
NADH + H+
NAD+
Palmitoleic acid (16:∆9); monounsaturated; monoenoicomega-7
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XVIII. ANOTHER EXAMPLE OF FATTY ACID DESATURATION
O ||
CH3-CH2-CH2- CH2- CH2- CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-C-O18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
O
||
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH= CH- CH2-CH2-CH2-CH2-CH2-CH2-CH2-C-O18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Stearic acid (C18:0); saturatedO2
2 H2O
∆9 desaturase
NADH + H+
NAD+
Oleic acid (18:∆9); monounsaturated; monoenoicomega-9
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XIX. EXAMPLE OF FATTY ACID ELONGATION AND DESATURATION
O
||CH3–CH2- CH2- CH2–CH2–CH = CH-CH2-CH = CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-C-S-CoA18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
O2
2 H2O∆6 desaturase
Linoleoyl CoA (18: 2∆9,12); dienoic
NADH+ + H+
NAD+
O
||CH3–CH2- CH2- CH2–CH2–CH = CH-CH2-CH = CH-CH2-CH = CH-CH2-CH2-CH2-CH2-C-S-CoA18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
γ-Linolenoyl CoA (18: 3∆6,9,12); trienoicMalonyl CoA
CO2 + HS-CoA
Elongase
O
||CH3-CH2-CH2-CH2-CH- CH=CH-CH2-CH=CH2-CH2-CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-C-S-CoA20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Eicosatrienoyl CoA (20: 3∆8,11,14); trienoic
O ||
CH3-CH2-CH2-CH2-CH- CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-CH2-CH2-C-S-CoA20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Arachidonoyl CoA (20: 4∆5,8,11,14); tetraenoic, omega-6
O2
2 H2O∆5 desaturase
NADH+ + H+
NAD+
Methylene groups
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XX. HUMAN DESATURATION OF
FATTY ACIDS
CH3-(CH2)6+n - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 – (CH2)2 -COOH Δ
4 des
atur
ase
Δ5 d
esat
uras
e
Δ6 de
satu
rase
Δ9 de
satu
rase
9
8
7
6
3
2
5
4
1
16
15 - 10
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XXI. CAN HUMANS SYNTHESIZE THESE TWO
FATTY ACIDS?
A. CH3 -(CH2)4-CH=CH-CH2-CH=CH-(CH2)7- COOH
B. CH3 -(CH2)4-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)4- COOH5
8 1911 1017 13 1218
8 19 7 612 101118 1317
Omega-6
Omega-6
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REFERENCES
Horton, Principles of Biochemistry, 4th ed. Devlin, Textbook of Biochemistry, 7th ed. Lippincott’s Biochemistry, 4th ed. Harper’s Illustrated Biochemistry, 28th ed.