Lipid Synthesis Biosynthesis of Fatty Acids & Lipids

ANABOLIS II: Biosynthesis of Fatty Acids & Lipids Fatty Acid Biosynthesis Animals can do, plants can do Omega 3 D15 Eicosanoids: Synthesis and Classes D6 desaturation elongation desaturation • Linoleate (18:2(Δ9,12) gets desaturated on both sides = γ-linolenate (18:3(Δ6,9,12) & α-linolenate (18:3(Δ9,12,15). • Elongation to C20, and further desaturation of γ-linolenate (18:3(Δ6,9,12) gives Arachidonate, 20:4(Δ5,8,11,14) hydroxylation elongation desaturation hydroxylation hydroxylation • Elongation to C20, and TWO further desaturation of α-linolenate (18:3(Δ9,12,15) gives EPA, 20:5(Δ5,8,11,14,17). More of the same gets DHA, 22:6(Δ4,7,10,13,16,19) • These desaturations are all going closer to the carboxylate and can be accomplished by animals. Eicosanoids (20C Polyunsaturated fatty acids (PUFAs)) bioactive paracrine From these signaling molecules are made: PG = Prostaglandins TX = Thromboxanes LT = Leukotrienes elongation elongation • Created from the arachidonate or EPA, which are incorporated into membranes phospholipids. • In response to stimuli (hormone, etc.), phospholipase A2 is activated • The unsaturated C-2 fatty acid is released Fatty Acid Biosynthesis Animals can do, plants can do Omega 3 D15 Eicosanoids: Synthesis and Classes D6 desaturation elongation desaturation (EET) • Elongation to C20, and further desaturation of γ-linolenate (18:3(Δ6,9,12) gives Arachidonate, 20:4(Δ5,8,11,14) hydroxylation (ARA) elongation desaturation hydroxylation • Linoleate (18:2(Δ9,12) gets desaturated on both sides = γ-linolenate (18:3(Δ6,9,12) & α-linolenate (18:3(Δ9,12,15). hydroxylation • Elongation to C20, and TWO further desaturation of α-linolenate (18:3(Δ9,12,15) gives EPA, 20:5(Δ5,8,11,14,17). More of the same gets DHA, 22:6(Δ4,7,10,13,16,19) • These desaturations are all going closer to the carboxylate and can be accomplished by animals. Eicosanoids (20C Polyunsaturated fatty acids (PUFAs)) bioactive paracrine From these signaling molecules are made: PG = Prostaglandins TX = Thromboxanes LT = Leukotrienes • Created from the arachidonate or EPA, which are incorporated into membranes phospholipids. • In response to stimuli (hormone, etc.), phospholipase A2 is activated • The unsaturated C-2 fatty acid is released Fatty Acid Biosynthesis Eicosanoids: Cyclic Pathway • PGH2 synthase (cyclooxygenase, or COX) has isozymes • COX-1 is ubiquitous and catalyzes synthesis of prostaglandins that regulate gastric mucin secretion and other smooth muscle functions • COX-2 is inducible (except in brain) by immune response and acts at the sites of inflammation. It catalyzes synthesis of prostaglandins that mediate pain, inflammation, and fever. Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit COX isozymes • Aspirin (acetylsalicylate) is an irreversible inhibitor. – acetylates a Ser in active site – blocks active site in both COX isozymes PGH2 synthase is a cyclooxygenase/peroxidase enzyme that functions in the smooth ER. • Ibuprofen, naproxen, and indomethacin are competitive inhibitors. •Step 1: PGH2’s cyclooxygenase activity adds 2 O2 to form PGG2. – resemble substrate; also block active site in both isozymes •Step 2: PGH2’s peroxidase activity converts peroxide to alcohol, creates PGH2. Bengt Samuelsson Nobel Prize 1982 Celebrex Indomethacin • Celebrex and Vioxin are specific for COX-2 Fatty Acid Biosynthesis Different Series EET (3) ARA(4) PGE1 Prostaglandin & Thromboxane: Synthesis and Classes PGF1 a Different Classes PGE2 PGF2 a EPA (5) Series 1 Series 2 PGF3 a PGE3 PG = Prostaglandins/TB=Thromboxane –letters-after are for number and oxidation state of oxygens and ring –subscript is the number of double bonds Series 2 prostaglandins have important roles in the immediate response to stress or injury, including inflammation, Fatty Acid Biosynthesis Thromboxane: Synthesis and Classes TB=Thromboxane –letters after are for number and oxidation state of oxygens and ring –subscript is the number of double bonds Platelet aggregation and wound healing Fatty Acid Biosynthesis Eicosanoids: Linear Pathway Synthesis of Leukotrienes /peroxidase (LOX) 3-lipoxygenase (3-LOX) LOX LTA4 Hepoxilin A3 GSH glutathione-Stransferase Psoriasis •O2 added to arachidonate via lipoxygenases (mixedLTB function oxidases) (LOX) •Creates species that differ in the position of the OOH group •LOX enzymes are found in leukocytes and in heart, brain, lung, and spleen, are mixed-function oxidases of the cytochrome P-450 family. •Inflammatory chemicals released after contact with an allergen; airways constrict, excess mucus and fluid produced (e.g., asthma; difficult to breathe). 4 LCC4 g-glutamyl transpeptidase Glu LCD4 Gly cysteinyl-glycine dipeptidase LTE4 ANABOLISM II: Biosynthesis of Fatty Acids & Lipids Lipid Biosynthesis Fatty Acid Synthesis Fat Catabolism Fatty Acid Degradation Ketone body Utilization Lipid Biosynthesis Biosynthesis of Triacylglycerol Fat (Triacylglycerol) and Phospholipids in Animals, Plants, and Bacteria have a common intermediate: Phosphophatidic Acid Usually saturated FA Lysophosphatidate Usually unsaturated FA • Animals and plants store fat for fuel. – plants: in seeds, nuts – typical 70-kg human has ~15 kg fat • enough to last 12 weeks • compare with 12 hours worth of glycogen in liver and muscle • All organisms make glycerophospholipids for membranes. • Both molecules contain glycerol from Glycerol 3-P • Most Glycerol 3-P comes from dihydroxyacetone phosphate (DHAP) in glycolysis. – via glycerol 3-phosphate dehydrogenase • Minor amount from glycerol (liver and kidney). Phosphatidate 1,2 Diacylglycerol – via glycerol kinase • Phosphatidic acid is the precursor to fat and glycerophospholipids. – fatty acids attached by acyl transferases – releases CoA Triacylglycerol Lipid Biosynthesis Regulation of Triacylglycerol Synthesis by Insulin • Secretion of Insulin results in stimulation of triacylglycerol synthesis. • Lack of insulin results in: Fat ▲ –increased lipolysis –increased fatty acid oxidation Fatty Acids • And when citric acid cycle intermediates (oxaloacetate) are depleted (as in diabetes when glucose cannot get in), acetylCoA builds up and ketones bodies are made –Repression of fatty acid synthase (no Protein Phosphatase 2A) –ACC is not active (remains phosphorylated) –No malonyl-CoA means boxidation is active b-oxidation Fatty Acid Synthase Diabetics prone to metabolic ketosis and acidosis Lipid Biosynthesis Triacylglycerol Cycle is a seemingly Futile Cycle • Seventy-five percent of free fatty acids (FFAs) released by lipolysis are re-esterified to form TAGs, rather than be used for fuel. – Some recycling occurs in adipose tissue. – Some FFAs from adipose cells are transported to the liver, remade into TAG, and redeposited in adipose cells. • Although the distribution between these two paths may vary, overall, the percentage of FFAs being esterified remains at ~75%. Lipid Biosynthesis Biosynthesis of Membrane Phospholipds Glycerophospholipid Biosynthesis requires Attach head group by condensation here: Activation by CTP Phosphatidic acid • Begin with phosphatidic acid (microorganisms) or 1,2 Diacylglycerol (mammals) • Both activate precursors using CTP • Bacteria attach alcohol group to C-3 phosphate of phosphatidic acid – Make CDP-diacylglycerol from CTP and phosphatidic acid • Mammals use CDP-alcohol and attach Example: head group to diacylglycerol – Make CDP-alcohol from CTP and choline or ethanolamine mammals bacteria Lipid Biosynthesis Biosynthesis of Membrane Phospholipds Glycerophospholipid Biosynthesis requires Attach head group by condensation here: Activation by CTP Phosphatidic acid • Begin with phosphatidic acid (microorganisms) or 1,2 Diacylglycerol (mammals) • Both activate precursors using CTP • Bacteria attach alcohol group to C-3 phosphate of phosphatidic acid – Make CDP-diacylglycerol from CTP and phosphatidic acid • Mammals use CDP-alcohol and attach Example: head group to diacylglycerol – Make CDP-alcohol from CTP and choline or ethanolamine Lipid Biosynthesis Glycerophospholipid Synthesis in E. coli • For Phosphatidylserine and phosphatidylinositol, the free alcohol does a nucleophilic attack on the CDP-activated phosphatidate. • Phosphatidylserine is decarboxylated to phosphatidylethanolamine. • enzyme is phosphatidylserine decarboxylase • Phosphatidylethanolamine acted on by S-adenosylmethionine (SAM) adds three methyl groups to amino group à phopshatidylcholine (lecithin). • catalyzed by methyltransferase • Cardilipin is from the condensation of two phosphatidyl glycerols, which are formed from glycerol 3-phosphate. mammals bacteria Lipid Biosynthesis Biosynthesis of Membrane Phospholipds Glycerophospholipid Biosynthesis requires Attach head group by condensation here: Activation by CTP • Begin with phosphatidic acid (microorganisms) or 1,2 Diacylglycerol (mammals) • Both activate precursors using CTP • Bacteria use phosphatidate and attach head group to C-3 phosphate group mammals bacteria – Make CDP-diacylglycerol from CTP and phosphatidic acid • Mammals use CDP-alcohol and attach Example: head group to diacylglycerol – Make CDP-alcohol from CTP and choline or ethanolamine Lipid Biosynthesis Synthesis of Phosphatidylcholine, -ethanolamine, and serine and in Mammals • Alcohols are activated (phosphorlyation) then attached to CMP. Mammals use CDP-alcohol • CDP-alcohol is used to couple this to diacylglycerol • Phosphatidyl-serine is made “backwards” from phosphatidyl-ethanolamine or phosphatidyl-choline via head-group exchange reactions. • catalyzed by specific synthases • pathway “salvages” the choline Cholesterol and Steroid Biosynthesis Fates of Acetyl CoA (HMG-CoA) Amino acids Amino acid (L) 1. Oxidation to CO2 2. Lipid metabolism Fattyacid acids metabolism 3. 1. Amino 2. Ketone bodies & cholesterol 3. Amino acid metabolism Cholesterol and Steroid Biosynthesis “Fat burns in the flame of sugar” Fatty Acids NADH Acetyl-CoA NADH FADH2 Pyruvate Pyruvate CO2 Citrate Oxaloacetate Malate Isocitrate a -Ketoglutarate Fumarate Succinyl-CoA Succinate Ketone Bodies Cholesterol and Steroid Biosynthesis Ketone Body Biosynthesis • The first step is reverse of the last step in the b oxidation: thiolase reaction joins two acetate units. • A third acetyl-CoA is incorporated in the second step. • Together, two CoASH are freed from three acetyl-CoA. • In the liver, this synthesis occurs regardless of excess acetyl-CoA • Also synthesized from Leucine • HMG-CoA is a metabolic junction Cholesterol and Steroid Biosynthesis Ketone Body Biosynthesis • The first step is reverse of the last step in the b oxidation: thiolase reaction joins two acetate units. • A third acetyl-CoA is incorporated in the second step. • Together, two CoASH are freed from three acetyl-CoA. • In the liver, this synthesis occurs regardless of excess acetyl-CoA • Also synthesized from Leucine • HMG-CoA is a metabolic junction Cholesterol and Steroid Biosynthesis Ketone Body Biosynthesis • In order to traffic to other tissues, CoA must be removed. This is done by removing as acetyl-CoA leaving Acetoacetate. This along with Acetone and b-hydroxybutyrate can then travel through the blood to other tissues for energy (catabolism). Ø In the mitochondria • Acetone is removed as a gas and exhaled (although some species or tissues can metabolize acetone), but acetoacetate and b-hydroxybutyrate can traffic to the heart, kidney, muscle, and adapted brain for use in energy production. Cholesterol and Steroid Biosynthesis 4.5’ Ketone Body Biosynthesis From HMG-CoA HMG-CoA & ketone bodies: