De Novo Synthesis of Fatty Acids
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Transcript of De Novo Synthesis of Fatty Acids
DE NOVO SYNTHESISOF
FATTY ACIDSFloro B. Madarcos, MDDept. of Biochemistry
URMMMC College of Medicine
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
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.
DE NOVO SYNTHESIS OFFATTY ACIDS
II. Cellular Location
Cytoplasm
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
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
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
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
REACTIONS OF FATTY ACIDSYNTHASE
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
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)
VII. SOURCES OF NADPH2 FOR FATTY ACID
SYNTHESISPentose Phosphate Pathway
(HMP)Cytosolic conversion of malate to
pyruvateExtramitochondrial isocitrate
dehydrogenase - ruminants
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
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
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
X. BALANCE SHEET FOR THE CONVERSION OF ACETYL CoA
TO PALMITATE
8Acetyl CoA + 7Malonyl CoA + 14NADPH
+ 14H+
1Palmitate + 7CO2 + 8CoA + 14NADP+ + 6H2O
XI. PAMITATE MODIFICATION
Chain Elongation Desaturation Hydroxylation
XII. PAMITATE MODIFICATION
Sites ER – Malonyl CoA/ NADPH/
Palmitoyl CoA Mitochodrion – Acetyl CoA,
NAD & NADPH
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
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.
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
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)
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
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
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
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
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
REFERENCES
Horton, Principles of Biochemistry, 4th ed. Devlin, Textbook of Biochemistry, 7th ed. Lippincott’s Biochemistry, 4th ed. Harper’s Illustrated Biochemistry, 28th ed.