Slide 1

Synthesis and degradation of fatty acids Zdeka Kluskov Slide 2 Fatty acids (FA) mostly an even number of carbon atoms and linear chain in esterified form as component of lipids in unesterified form in plasmabinding to albumin Groups of FA: according to the number of double bonds no double bond one double bond more double bonds saturated FA (SAFA) monounsaturated FA (MUFA) polyunsaturated FA (PUFA) according to the chain length C 20 short-chain FA (SCFA) medium-chain FA (MCFA) long-chain FA (LCFA) very-long-chain FA (VLCFA) Slide 3 Overview of FA Slide 4 Triacylglycerols main storage form of FA acylglycerols with three acyl groups stored mainly in adipose tissue Slide 5 function:energy storage in the form of TAG acyl-CoA and glycerol-3-phosphate TAG incorporation into very low density lipoproteins (VLDL) entry of VLDL into the blood circulation TAG transport from the liver to other tissues via VLDL synthesis of TAG in liver (especially skeletal muscle, adipose tissue) FA biosynthesis in the excess of energy (increased caloric intake) FA biosynthesis Slide 6 mainly in the liver, adipose tissue, mammary gland during lactation localization: cell cytoplasm (up to C 16 ) endoplasmic reticulum, mitochondrion enzymes: acetyl-CoA-carboxylase(HCO 3 - - source of CO 2, biotin, ATP) fatty acid synthase(NADPH + H +, pantothenic acid) primary substrate: acetyl-CoA final product: palmitate (elongation = chain extension) (always in excess calories) FA biosynthesis Slide 7 repeated extension of FA by two carbons in each cycle on the multienzyme complex FA synthase to the chain length C 16 (palmitate) palmitate, a precursor of saturated and unsaturated FA: saturated FA (> C 16 )elongation systems unsaturated FA desaturation systems FA biosynthesis Slide 8 Acetyl-CoA1. source: oxidative decarboxylation of pyruvate (the main source of glucose) NADPH2. source: pentose phosphate pathway (the main source) the conversion of malate to pyruvate (NADP + -dependent malate dehydrogenase - malic enzyme) transport across the inner mitochondrial membrane as citrate the conversion of isocitrate to -ketoglutarate (isocitrate dehydrogenase) degradation of FA, ketones, ketogenic amino acids Precursors for FA biosynthesis Slide 9 Formation of malonyl-CoA HCO 3 - + ATPADP + P i enzyme-biotin enzyme-biotin-COO - enzyme-biotin acetyl-CoA malonyl-CoA biotinyl-enzymecarboxybiotinyl-enzyme + 1carboxylation of biotin2 transfer of carboxyl group to acetyl-CoA formation of malonyl-CoA enzyme acetyl-CoA-carboxylase FA biosynthesis Slide 10 Regulation at the level of ACC acetyl-CoAmalonyl-CoA palmitateglucosecitratepalmitoyl-CoA acetyl-CoA carboxylase protein kinase A AMP-dependent insulinAMP cAMP glucagonadrenaline FA biosynthesis protein kinase A Slide 11 FA synthase FA biosynthesis Slide 12 The course of FA biosynthesis acetyl-CoAmalonyl-CoA acetyltransacylase acyl(acetyl)-malonyl- CoASH transacylation -enzyme complex malonyltransacylase Slide 13 acyl(acetyl)-malonyl-enzyme complex 3-ketoacyl-enzyme complex 3-ketoacyl-synthase CO 2 condensation (acetacetyl-enzyme complex) FA biosynthesis The course of FA biosynthesis Slide 14 3-ketoacyl-enzyme complex (acetoacetyl-enzyme complex) 3-hydroxyacyl-enzyme complex NADPH + H + NADP + 3-ketoacyl-reductase H2OH2O 3-hydroxyacyl- dehydrase 2,3-unsaturated acyl-enzyme complexacyl-enzyme complex NADPH + H + NADP + enoylreductase first reductiondehydrationsecond reduction FA biosynthesis The course of FA biosynthesis Slide 15 Repetition of the cycle acyl-enzyme complex (palmitoyl-enzyme complex) CoASH malonyl-CoA FA biosynthesis Slide 16 The release of palmitate palmitoyl-enzyme complex H2OH2O + palmitate thioesterase FA biosynthesis Slide 17 The fate of palmitate after FA biosynthesis palmitatepalmitoyl-CoA acylglycerols cholesterol esters acyl-CoA esterification elongation desaturation acyl-CoA-synthetase ATP + CoA AMP + PP i FA biosynthesis Slide 18 FA elongation microsomal elongation system1. in the endoplasmic reticulum malonyl-CoA the donor of the C 2 units extension of saturated and unsaturated FA palmitic acid (C16) FA > C16 elongases (chain elongation) mitochondrial elongation system2. in mitochondria acetyl-CoA the donor of the C 2 unit NADPH + H + the donor of the reducing equivalents not reverse -oxidation FA biosynthesis fatty acid synthase Slide 19 Microsomal extension of FA acetyl-CoAmalonyl-CoA3-ketoacyl-CoA 3-hydroxyacyl-CoA 2,3-unsaturated acyl-CoA acyl-CoA CoASH + CO 2 NADPH + H + NADP + H2OH2ONADPH + H + NADP + + synthase reductase hydratase reductase CoASH + CO 2 + NADPH + H + NADP + H2OH2O NADPH + H + NADP + palmitoyl-CoAmalonyl-CoA stearoyl-CoA Example: FA biosynthesis Slide 20 FA desaturation in the endoplasmic reticulum process requiring O 2, NADH, cytochrome b 5 FA biosynthesis Slide 21 FA degradation function: major energy source (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 entry of FA into target cellsactivation to acyl-CoA transfer of acyl-CoA via carnitine system into mitochondria-oxidation Most important FA released from adipose tissue: palmitic acid oleic acid stearic acid Slide 22 long-chain FA (LCFA, C 12 C 20 ) unsaturated FA odd-chain-length FA very-long-chain FA (VLCFA, > C 20 ) FA with C 10 or C 12 long-chain branched-chain FA mitochondrial -oxidation modified peroxisomal -oxidation peroxisomal -oxidation -oxidation FA degradation Mechanisms of FA degradation Slide 23 -oxidation -oxidation -oxidation Mechanisms of FA degradation FA degradation Slide 24 mainly in muscles localization: mitochondrial matrix peroxisome enzymes: acyl CoA synthetase carnitine palmitoyl transferase I, II; carnitine acylcarnitine translocase substrate: acyl-CoA final products: acetyl-CoA -oxidation dehydrogenase (FAD, NAD + ), hydratase, thiolase propionyl-CoA FA degradation Slide 25 repeated shortening of FA by two carbons in each cycle oxidation of acetyl-CoA to CO 2 and H 2 O in the citric acid cycle generation of 8 molecules of acetyl-CoA from 1 molecule of palmitoyl-CoA cleavage of two carbon atoms in the form of acetyl-CoA complete oxidation of FA PRODUCTION OF LARGE QUANTITY OF ATP production of NADH, FADH 2 reoxidation in the respiratory chain to form ATP FA degradation -oxidation Slide 26 Activation of FA fatty acidATP pyrophosphate (PP i ) acyl-CoAAMP acyl-CoA-synthetase pyrophosphatase acyl adenylate fatty acid+ ATP + CoASH acyl-CoA + AMP + PP i PP i + H 2 O2P i FA degradation Slide 27 The role of carnitine in the transport of FA 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 FA degradation Slide 28 acyl-CoA trans- 2 -enoyl-CoA L--hydroxyacyl-CoA -ketoacyl-CoA acyl-CoAacetyl-CoA acyl-CoA-dehydrogenase enoyl-CoA-hydratase L--hydroxyacyl-CoA- -ketoacyl-CoA-thiolase Steps of cycle: dehydrogenation oxidation by FAD creation of unsaturated acid hydration addition of water on the -carbon atom creation of -hydroxyacid dehydrogenation oxidation by NAD + creation of -oxoacid cleavage at the presence of CoA formation of acetyl-CoA formation of acyl-CoA (two carbons shorter) -oxidation -dehydrogenase FA degradation Slide 29 Oxidation of unsaturated FA 3 acetyl-CoA3 rounds of -oxidation -oxidation 1 acetyl-CoA linoleoyl-CoA NADPH + H + NADP + enoyl-CoA-isomerase dienoyl-CoA-reductase acyl-CoA-dehydrogenase cis- 3, cis- 6 trans- 2, cis- 6 cis- 4 trans- 2, cis- 4 trans- 3 trans- 2 cis 9, cis- 12 4 rounds of -oxidation 5 acetyl-CoA the most common unsaturated FA in the diet: degradation of unsaturated FA by -oxidation to a double bond conversion of cis-isomer of FA by specific isomerase to trans-isomer continuation of -oxidation to the next double bond oleic acid, linoleic acid elimination of double bond between C 4 and C 5 by reduction formation of double bond between C 2 and C 3 by dehydrogenation intramolecular transfer of double bond continuation of -oxidation FA degradation Slide 30 Oxidation of odd-chain FA propionyl-CoA D-methylmalonyl-CoA L-methylmalonyl-CoA succinyl-CoA HCO 3 - + ATP ADP + P i propionyl-CoA carboxylase (biotin) methylmalonyl-CoA mutase (B 12 ) methylmalonyl-CoA racemase shortening of FA to C 5 formation of acetyl-CoA and propionyl-CoA carboxylation of propionyl-CoA epimerization of D-form into L-form intramolecular rearrangement to form succinyl-CoA entry of succinyl-CoA into the citric acid cycle stopping of -oxidation FA degradation Slide 31 Peroxisomal oxidation of FA A) very-long-chain FA (VLCFA, > C 20 ) Differences between -oxidation in the mitochondrion and peroxisome: 1. step dehydrogenation by FAD mitochondrion: electrons from FADH 2 are delivered to the respiratory chain where they are transferred to O 2 to form H 2 O and ATP peroxisome: electrons from FADH 2 are delivered to O 2 to form H 2 O 2, which is degraded by catalase to H 2 O and O 2 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 transport of acyl-CoA into the peroxisome without carnitine FA degradation Slide 32 Differences between -oxidation in the mitochondrion and peroxisome: 4. step cleavage at the presence of CoA mitochondrion: metabolization in the citric acid cycle peroxisome: export to the cytosol, to the mitochondrion (oxidation) acetyl-CoA a precursor for the synthesis of cholesterol and bile acids a precursor for the synthesis of fatty acids of phospholipids Peroxisomal oxidation of FA FA degradation Slide 33 B) long-chain branched-chain FA blocking of -oxidation by the alcyl group at C -oxidation hydroxylation at C cleavage of the original carboxyl group as CO 2 methyl group is in the position transfer of FA in the form of acylcarnitine into the mitochondrion shortening of FA to 8 carbons complete of -oxidation in the mitochondrion Peroxisomal oxidation of FA FA degradation Slide 34 Refsum's disease rare autosomal recessive hereditary disease phytanic acid a product of metabolism of phytol (part of chlorophyll) in milk and animal fats decreased activity of peroxisomal -hydroxylaseaccumulation of phytanic acid (in tissues of nervous system and serum) ataxia, night blindness, hearing loss, skin changes etc. Slide 35 -oxidation of FA minor pathway of FA oxidation in the endoplasmatic reticulum repeated oxidation of -carbon -CH 3 - CH 2 OH -COOH formation of dicarboxylic acid entry of dicarboxylic acid into -oxidation reduction of FA to adipic acid (C 6 ) or suberic acid (C 8 ) excreted in the urine FA degradation Slide 36 Regulation of -oxidation acetyl-CoAmalonyl-CoACPT I -oxidation ACC A) by energy demands of cell by the level of ATP and NADH: FA can not be oxidized faster than NADH and FADH 2 are reoxidized in the respiratory chain B) via carnitine palmitoyl transferase I (CPT I) CPT I is inhibited by malonyl-CoA, which is generated in the synthesis of FA by acetyl-CoA carboxylase (ACC) active FA synthesisinhibition of -oxidation FA degradation Slide 37 Comparison of FA biosynthesis and FA degradation Slide 38 in the liver localization: mitochondrial matrix substrate: acetyl-CoA products: acetone acetoacetate D--hydroxybutyrate conditions: in excess of acetyl-CoA function: energy substrates for extrahepatic tissues Ketone bodies Ketogenesis Slide 39 Ketone bodies Ketogenesis Slide 40 acetoacetate spontaneous decarboxylation to acetone conversion to D--hydroxybutyrate by D--hydroxybutyrate dehydrogenase waste product (lung, urine) energy substrates for extrahepatic tissues Ketone bodies Ketogenesis Slide 41 Utilization of ketone bodies citric acid cycle energy source for extrahepatic tissues (especially heart and skeletal muscle) in starvation - the main source of energy energy production water-soluble FA equivalents Ketone bodies for the brain Slide 42 Production, utilization and excretion of ketone bodies acetyl-CoA oxidation in the citric acid cycle (liver) conversion to ketone bodies release of ketone bodies into blood transport to tissues Ketone bodies (liver - mitochondrion) Slide 43 lipolysis FA in plasma -oxidation excess of acetyl-CoA ketogenesis increased ketogenesis: starvation prolonged exercise diabetes mellitus high-fat diet low-carbohydrate diet utilization of ketone bodies as an energy source to spare of glucose and muscle proteins (skeletal muscle, intestinal mucose, adipocytes, brain, heart etc.) Ketogenesis Ketone bodies Slide 44 http://www.hindawi.com/journals/jobes/2011/482021/fig2/ Marks, A.; Lieberman, M. 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