Synthesis of Fatty Acids and Triacylglycerol Lippincott s Chapter 16 Fatty Acid Synthesis Mainly in the Liver Requires Carbon Source: Acetyl CoA Reducing Power: NADPH 8 CH 3 COO C 15 H 33 COO Energy Input: ATP 1
Why Energy? Fatty Acid Acetyl CoA G o : -ve Acetyl CoA Fatty Acid G o : +ve Why Energy? Fatty Acid Acetyl CoA G o : -ve Acetyl CoA + n(atp) Fatty Acid + n(adp) G o : -ve 2
FA Degradation and Synthesis Acyl CoA (n) Oxidation Acyl CoA (n+2) reduction Hydration Oxidation Thyolysis dehydration reduction condensation Acyl CoA (n-2) + Acetyl CoA Acyl CoA (n) + Malonyl CoA AcetylCoA Carboxylation of Acetyl CoA Produces Malonyl CoA O O O װ װ װ CH 3 -C-CoA - OC-CH 2 -C-CoA CO 2 ATP ADP + Pi Acetyl CoA Carboxylase Biotin-Containing Enzyme 3
Fatty Acid Synthase Catalyzes the remaining steps Multifunctional Enzyme Complex Dimer of two Identical Chains Each has Seven Catalytic Activities One activity is Condensing Enzyme with SH One Domain is known as Acyl Carrier Protein Carries Intermediates during Catalysis (Acyl, Acetyl and Malonyl Groups) A protein joined to Phosphopantheine group Reactive SH group Phosphopantetheine group is part of ACP and? phosphate β-mercapto ethylamine Adenine Ribose Protein Pantothenic acid 4
Fatty Acid Synthesis (Overview) Acetyl-CE (Acyl-CE) + Malonyl ACP (n) (3) Ketoacyl ACP (n+2) Acyl ACP CO 2 CH 3 CO~S-CE Acetyl (Acyl) + OOC-CH 2 -CO~ACP Malonyl-ACP CO 2 HS-CE O CH 3 C-CH 2 -CO~ACP Ketoacyl- ACP 5
Reduction of the Ketoacyl Group O CH 3 C-CH 2 -CO~ACP NADPH Ketoacyl- ACP H 2 O OH l CH 3 CH-CH 2 - CH 3 CH=CH- NADPH CH 3 CH 2 -CH 2 -CO~ACP Synthesis of Palmitate by Fatty Acid Synthase 6
Synthesis of Palmitate by Fatty Acid Synthase (Cont.) Synthesis of Palmitate (net reaction) How many cycles of synthesis (Condensation)? * 7 How many Malonyl CoA? * 7 How many Acetyl CoA? * 1 How Many NADPH? * 14 7
Production of Cytosolic Acetyl CoA for FA Synthesis Inner mitochondrial membrane is immpermiable to Acetyl CoA NADH NAD + Production of NADPH o Pentose Phosphate Pathway o NADP- dependent malate Dehydrogenase NADPH The Fate of Oxaloacetate 8
Return of Oxaloacetate Pyruvate + CO2 NADPH NADP + Malate NAD + Regulation of FA Oxidation & Synthesis OXIDATION Supply of Fatty Acids -Hormonal Control Entry into Mitochondria Availability of NAD + SYNTHESIS Regulation of AcCoA Carboxylase -Allosteric Mechanism - Phosphorylation Amounts of Enzymes 9
Allosteric Regulation of Acetyl CoA Carboxylase Hormone-Mediated, Covalent Regulation of Acetyl CoA Carboxylase ACC 10
Regulation of FA Oxidation & Synthesis OXIDATION Supply of Fatty Acids -Hormonal Control Entry into Miochondria Availability of NAD + SYNTHESIS Regulation of AcCoA Carboxylase -Allosteric Mechanism - Phosphorylation Amounts of Enzymes Regulation of FA Oxidation Fatty Acids Fatty Acyl CoA NADH - Fatty Acyl Carnitine - Malonyl CoA ACC Acetyl CoA Acetyl CoA 11
Elongation of Fatty Acids -in Endoplasmic Reticulum - Similar Sequence of Reactions - Different Enzymes Malonyl CoA + Acyl CoA ( n) 2NADPH + H + 2NADP + Acyl CoA (n+2) n = 16 or more carbons Elongation of Fatty Acids in Mitochondria Acetyl CoA + Acyl CoA (n) NADH + H+ NAD+ Acyl CoA (n+2) n = less than16 carbons NADPH NADP+ 12
Introduction of Double Bonds Synthesis of Monounsaturated FA - Oleic Acid 18: 9 - Palmitoleic 16: 9 In endoplasmic reticulum No double bond can be introduced beyond carbon 9 in human Introduction of Double Bonds (Cont.) Stearoyl CoA Palmitoyl CoA NADPH + O 2 Oleoyl CoA NADP + +2H 2 O Palmitoleoyl CoA 9 Desaturase; Cytochrome b 5 13
Introduction of Double Bonds (Cont.) Stearoyl CoA Palmitoyl CoA NADPH + O 2 Oleoyl CoA NADP + +2H 2 O Palmitoleoyl CoA 9 Desaturase; Cytochrome b 5 Introduction of Double Bonds (Cont.) Formation and Modification of Polyunsaturated FA -Elongation - Desaturation Additional double bonds can be introduced by: 4 Desaturase 5 Desaturase 6 Desaturase 14
Modification of Polyunsaturated FA Linoleic 18:2 9,12 Desaturation 18:3 6,9,12 ω? 20:3 8,11,14 ω? Elongation Desaturation 20:4 5,8,11,14 ω? Arachidonic Biosynthesis of Triacylglycerol & Phosphoacylglycerol G L Y C E R O L FATTY ACID FATTY ACID FATTY ACID G L Y C E R O L PHOSPHATE FATTY ACID FATTY ACID ALCOHOL TRIACYLGLYCEROL PHOSPHOACYLGLYCEROL 15
Phosphotadic Acid is Common Intermediate FATTY ACID G L Y C E R O L PHOSPHATE FATTY ACID PHOSPHOACYLGLYCEROL Biosynthesis of Triacylglycerol Requires Acyl~CoA (Active form of FA) Glycerol Phosphate Why Active form? TAG + H 2 O DAG + FA G ve DAG + FA TAG + H 2 O G +ve DAG + Acyl~CoA TAG + CoA G ve 16
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Production of Glycerol Phosphate - Glycerol + ATP --- Glycerol 3 Phosphate Enz: Glycerol Kinase Not in Adipose tissue CH 2 OH CH 2 OH I I C = O C HOH I I CH 2 OPO 3 CH 2 OPO 3 NADH NAD + Production of Glycerol Phosphate 18
Glucose DHAP Glycerol- P FA~CoA TAG Glycerol + Fatty Acids 19