Synthesis and degradation of fatty acids Martina Srbová

Transcription

1 Synthesis and degradation of fatty acids Martina Srbová

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 plasma binding to albumin Groups of FA: according to the chain length <C 6 C 6 C 12 C 14 C 20 >C 20 according to the number of double bonds no double bond one double bond more double bonds short-chain FA (SCFA) medium-chain FA (MCFA) long-chain FA (LCFA) very-long-chain FA (VLCFA) saturated FA (SAFA) monounsaturated FA (MUFA) polyunsaturated FA (PUFA)

3 Overview of FA

4 FA biosynthesis mainly in the liver, adipose tissue, mammary gland during lactation (always in excess calories) localization: cell cytoplasm (up to C 16 ) endoplasmic reticulum, mitochondrion (elongation = chain extension) enzymes: acetyl-coa-carboxylase (HCO source of CO 2, biotin, ATP) fatty acid synthase (NADPH + H +, pantothenic acid) primary substrate: acetyl-coa final product: palmitate

5 Precursors for FA biosynthesis 1. Acetyl-CoA source: oxidative decarboxylation of pyruvate (the main source of glucose) degradation of FA, ketones, ketogenic amino acids transport across the inner mitochondrial membrane as citrate 2. NADPH source: pentose phosphate pathway (the main source) the conversion of malate to pyruvate (NADP + -dependent malate dehydrogenase - malic enzyme ) the conversion of isocitrate to α-ketoglutarate (isocitrate dehydrogenase)

6 Precursors for FA biosynthesis Acetyl-CoA + HSCoA OAA - oxaloacetate

7 FA biosynthesis Formation of malonyl-coa catalysed by acetyl-coa-carboxylase (ACC) HCO ATP ADP + P i enzyme-biotin enzyme-biotin-coo - 1 carboxylation of biotin 2 transfer of carboxyl group to acetyl-coa acetyl-coa formation of malonyl-coa + enzyme-biotin enzyme acetyl-coa-carboxylase malonyl-coa

8 FA biosynthesis on the multienzyme complex FA synthase repeated extension of FA by two carbons in each cycle to the chain length C 16 (palmitate) ACP acyl carrier protein

9 FA biosynthesis The course of FA biosynthesis acetyl-coa malonyl-coa CoASH CoASH acetyltransacylase malonyltransacylase transacylation acyl(acetyl)-malonyl- -enzyme complex

10 FA biosynthesis The course of FA biosynthesis 3-ketoacyl-synthase CO 2 condensation acyl(acetyl)-malonyl-enzyme complex 3-ketoacyl-enzyme complex (acetacetyl-enzyme complex)

11 FA biosynthesis The course of FA biosynthesis NADPH + H + NADP + NADPH + H + NADP + 3-ketoacyl-reductase H 2 O 3-hydroxyacyldehydrase enoylreductase first reduction dehydration second reduction 3-ketoacyl-enzyme complex (acetoacetyl-enzyme complex) 3-hydroxyacyl-enzyme complex 2,3-unsaturated acyl-enzyme complex acyl-enzyme complex

12 FA biosynthesis Repetition of the cycle malonyl-coa CoASH acyl-enzyme complex (palmitoyl-enzyme complex)

13 FA biosynthesis The release of palmitate thioesterase H 2 O + palmitate palmitoyl-enzyme complex

14 FA biosynthesis The fate of palmitate after FA biosynthesis acylglycerols ATP + CoA AMP + PP i esterification cholesterol esters palmitate acyl-coa-synthetase palmitoyl-coa elongation desaturation acyl-coa

15 FA biosynthesis FA elongation 1. microsomal elongation system in the endoplasmic reticulum malonyl-coa the donor of the C 2 units NADPH + H + the donor of the reducing equivalents extension of saturated and unsaturated FA FA > C16 elongases (chain elongation) palmitic acid (C16) fatty acid synthase 2. mitochondrial elongation system in mitochondria acetyl-coa the donor of the C 2 unit

16 FA biosynthesis FA desaturation in the endoplasmic reticulum enzymes: desaturase, NADH-cyt b5-reductase process requiring O 2, NADH, cytochrome b 5 4 desaturases: double bonds at position 4,5,6,9 linoleic, linolenic essential FA stearoyl-coa + NADH + H + + O 2 oleoyl-coa + NAD + + 2H 2 O

17 FA biosynthesis - summary Formation of malonyl-coa Acetyl-CoA-carboxylase FA synthesis Palmitic acid FA Synthase cytosol Saturated fatty acids(>c16) Elongation systems- mitochondria, ER Unsaturated fatty acids Desaturation system - ER -

18 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 1 2 entry of FA into target cells activation to acyl-coa 3 transfer of acyl-coa via carnitine system into mitochondria 4 β-oxidation 5 In the liver, acetyl CoA is converted to ketone bodies

19 FA degradation -carbon β-carbon -carbon -oxidation C10, C12 β-oxidation -oxidation Branched FA VLCFA

20 FA degradation β-oxidation mainly in muscles localization: mitochondrial matrix peroxisome (VLCFA) enzymes: acyl CoA synthetase carnitine palmitoyl transferase I, II; carnitine acylcarnitine translocase dehydrogenase (FAD, NAD + ), hydratase, thiolase substrate: acyl-coa final products: acetyl-coa propionyl-coa

21 FA degradation β-oxidation repeated shortening of FA by two carbons in each cycle cleavage of two carbon atoms in the form of acetyl-coa oxidation of acetyl-coa to CO 2 and H 2 O in the citric acid cycle complete oxidation of FA generation of 8 molecules of acetyl-coa from 1 molecule of palmitoyl-coa production of NADH, FADH 2 reoxidation in the respiratory chain to form ATP PRODUCTION OF LARGE QUANTITY OF ATP

22 FA degradation Activation of FA fatty acid ATP acyl-coa-synthetase acyl adenylate pyrophosphate (PP i ) acyl-coa-synthetase pyrophosphatase 2P i acyl-coa AMP fatty acid+ ATP + CoASH PP i + H 2 O acyl-coa + AMP + PP i 2P i

23 FA degradation The role of carnitine in the transport of LCFA 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

24 FA degradation 3-hydroxy-4-N-trimethylaminobutyrate Carnitine Sources: Exogenous: meat, dairy products Endogenous: synthesis from lysine and methionine Transported into the cell by specific transporter Deficiency: Decreased transport of acyl-coa into mitochondria lipids accumulation myocardial damage muscle weakness Increased utilization of Glc hypoglycemia Similar symptoms are the genetically determined deficiency carnitinpalmitoyltransferase I or II

25 FA degradation β-oxidation Steps of cycle: acyl-coa dehydrogenation acyl-coa-dehydrogenase oxidation by FAD creation of unsaturated acid trans-δ 2 -enoyl-coa hydration enoyl-coa-hydratase addition of water on the β-carbon atom creation of β-hydroxyacid L-β-hydroxyacyl-CoA dehydrogenation L-β-hydroxyacyl-CoA- -dehydrogenase oxidation by NAD + creation of β-oxoacid β-ketoacyl-coa cleavage at the presence of CoA β-ketoacyl-coa-thiolase formation of acetyl-coa formation of acyl-coa (two carbons shorter) acyl-coa acetyl-coa

26 FA degradation Oxidation of unsaturated FA the most common unsaturated FA in the diet: oleic acid, linoleic acid β-oxidation of oleic acids degradation of unsaturated FA by β-oxidation to a double bond Unsaturated FA are cis isomers - aren t substrate for enoyl-coa hydratase conversion of cis-isomer of FA by specific isomerase to trans-isomer intramolecular transfer of double bond from β- to - β position continuation of β-oxidation 3 rounds of β-oxidation Normal intermediates of β-oxidation

27 FA degradation Oxidation of odd-chain FA shortening of FA to C 5 stopping of β-oxidation propionyl-coa HCO ATP formation of acetyl-coa and propionyl-coa propionyl-coa carboxylase (biotin) ADP + P i carboxylation of propionyl-coa methylmalonyl-coa intramolecular rearrangement to form succinyl-coa methylmalonyl-coa mutase (B 12 ) entry of succinyl-coa into the citric acid cycle succinyl-coa

28 FA degradation Peroxisomal oxidation of VLCFA Very-long-chain FA (VLCFA, > C 20 ) transport of acyl-coa into the peroxisome without carnitine Differences between β-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

29 FA degradation Peroxisomal oxidation of VLCFA Differences between β-oxidation in the mitochondrion and peroxisome: 4. step cleavage at the presence of CoA acetyl-coa mitochondrion: metabolization in the citric acid cycle peroxisome: export to the cytosol, to the mitochondrion (oxidation) a precursor for the synthesis of cholesterol and bile acids a precursor for the synthesis of fatty acids of phospholipids In peroxisome shortened FA bind to carnitine transfer acylcarnitine into mitochondrion acylcarnitine β-oxidation

30 FA degradation - oxidation Oxidation carbon ER liver, kidney mixed function oxidase Substrates C10 a C12 FA Products: dicarboxylic acids Excreted in the urine

31 Comparison of FA biosynthesis and FA degradation

32 Ketone bodies Ketogenesis increased ketogenesis: lipolysis starvation prolonged exercise diabetes mellitus high-fat diet low-carbohydrate diet utilization of ketone bodies as an energy source (skeletal muscle, intestinal mucose, adipocytes, brain, heart etc.) to spare of glucose and muscle proteins FA in plasma β-oxidation excess of acetyl-coa ketogenesis

33 Ketone bodies Ketogenesis in the liver localization: mitochondrial matrix substrate: acetyl-coa products: acetone acetoacetate D-β-hydroxybutyrate medium strength acids - ketoacidosis conditions: in excess of acetyl-coa function: energy substrates for extrahepatic tissues

34 Ketone bodies Ketogenesis

35 Ketone bodies Ketogenesis acetoacetate spontaneous decarboxylation to acetone conversion to D-β-hydroxybutyrate by D-β-hydroxybutyrate dehydrogenase waste product (lung, urine) energy substrates for extrahepatic tissues

36 Ketone bodies Utilization of ketone bodies water-soluble FA equivalents energy source for extrahepatic tissues (especially heart and skeletal muscle) in starvation - the main source of energy for the brain citric acid cycle energy production

37 Bibliography and sources Devlin, T. M. Textbook of biochemistry: with clinical correlations. 6th edition. Wiley-Liss, Marks, A.; Lieberman, M. Marks' basic medical biochemistry: a clinical approach. 3rd edition. Lippincott Williams & Wilkins, Matouš a kol. Základy lékařské chemie a biochemie. Galén, Meisenberg, G.; Simmons, W. H. Principles of medical biochemistry. 2nd edition. Elsevier, Murray et al. Harper's Biochemistry. 25th edition. Appleton & Lange,