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Fatty Acid Metabolism

Fatty Acid Metabolism. Free Energy of Oxidation of Carbon Compounds. Metabolic Motifs. Naming of Fatty Acids. Fatty acids differ in length and degree of saturation (number of double bonds) Double bonds can be in cis or trans

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Fatty Acid Metabolism

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  1. Fatty Acid Metabolism

  2. Free Energy of Oxidation of Carbon Compounds

  3. Metabolic Motifs

  4. Naming of Fatty Acids • Fatty acids differ in length and degree of saturation (number of double bonds) • Double bonds can be in cis or trans • in biological system double bonds are generally in cis conformation • Fatty acids are ionized at physiological pH

  5. Fatty Acid Metabolism • Triacylglycerols are concentrated energy stores • Utilization of FAs in 3 stages of processing (TAG -> FA; transport of FA; degradation of FA) • certain FAs require additional steps for degradation (unsaturated FA, odd-chain FA) • FA synthesis and degradation done by different pathways • Acetyl-CoA Carboxylase plays key role in controlling FA metabolism • Elongation and saturation of FAs are done by additional enzymes An adipocyte cell stores triacylglycerols in the cytoplasm

  6. Utilization of Fatty Acids requires 3 Stages of Processing: • Lipids (Triacylglycerols) are mobilizes -> broken down to fatty acids + glycerol • Fatty acids activated and transported into mitochondria • Fatty acids are broken down to acetyl-CoA -> citric acid cycle

  7. Dietary Lipids are Broken Down by Pancreatic Lipase and Transported through the LymphSystem

  8. Dietary Lipids are Broken Down by Pancreatic Lipase and Transported through the LymphSystem Packed together with Apoprotein B-48 ->to give Chylomicrons (180-500 nm in diameter)

  9. Mobilisation of Triacylglycerols That are Stored in Adipocyte Cells Lipolysis inducing hormones: Epinephrine, glucagon (low blood glucose level), adrenocorticotropic homones -> Insulin inhibits lipolysis Protein Kinase A phosphorylates (activates) -> Perilipin + HS lipase Perilipin (fat droplet associated protein) -> restructures fat to make it more accessible for lipase Free fatty acids and glycerol are released into the blood stream -> bound by serum albumin -> serves as carrier in blood Muscle cells

  10. Glycerol can be converted to Pyruvate or Glucose in the Liver !!! Conversion of: Glucose -> Glycerol possible !!! Intermediates in Glycolysis ands Glyconeogensesis Convertion of: Glucose -> Acetyl-CoA -> Fatty acid -> Fatpossible !!! Convertion of: Fat -> fatty acids -> Acety-CoA -> Glucoseimpossible !!!

  11. 1. Fatty Acid Activation - Fatty Acid Degradation

  12. 2. Transport of Fatty Acids into the Mitochondria Symptoms for deficiency of carnitine: mild muscle cramping -> weakness -> death

  13. Fatty Acid Oxidation (β-Oxidation Pathway) in the Mitochondria • 4 Steps in one round: • Oxidation -> introduction of double bond between α-β carbon, generation of FADH2 • Hydration of double bound • Oxidation of hydroxy (OH) group in β- position, generation of NADH • Thiolysis -> cleavage of 2 C units (acetyl CoA) Other oxidations: -> ω-Oxidation: in the endoplasmatic rediculum of liver and kidney many C-10 to C-12 carbons, normally not the main oxidation pathway -> if problems with β-oxidation -> α-Oxidation: in peroxisomes on branched FA (branch on β-carbon)

  14. Fatty Acid Oxidation (β-Oxidation Pathway) in the Mitochondria • Acyl CoA Dehydrogenase: • chain-length specific • FA with C-12 to C-18 -> long-chain isozyme • FA with C-14 to C-4 -> medium-chain isozyme • FA with C-4 and C-6 -> short-chain isozyme

  15. First 3 Rounds in Degradation of Palmitate (C-16): Complete oxidation of Palmitate -> 106 ATP Complete oxidation of Glucose -> 30 ATP

  16. Fatty Acid Oxidation in Peroxisomes Peroxisome in liver cell Fatty acid oxidation stops at Octanyl-CoA (C-8) -> may serve to shorten long chain to make them better suitable for β-Oxidation in mitochondria In Peroxisomes: Flavoprotein Acyl CoA dehydrogenase transfers electrons (not FADH2)

  17. Fatty Acid Oxidation in Peroxisomes Catalase regeneration in cytosol Acetyl-CoA produced in the peroxisomes -> used as precursors and not for energy consumption

  18. Enzymes of β-oxidation

  19. Oxidation of Monounsaturated FA and FA with odd-numbered double bonds

  20. Oxidation of Polyunsaturated Fatty Acids - 1 acetyl CoA

  21. Oxidation of Odd-Chain Fatty Acids -> Propionyl CoA In lipids from many plants and marine organisms Reaction requires Vitamin B12 (Cobalamin) Citric acid cycle

  22. Oxidation of Odd-Chain Fatty Acids -> Propionyl CoA Vitamin B12 : Animals and plants cannot produce B12 -> produced by a few species of bacteria living in the intestine Deficiency-> failure to absorb vitamine (not enough of the protein that facilitates uptake) -> reduced red blood cells, reduced level of hemoglobin, impairment of central nervous system Reaction requires Vitamin B12 (Cobalamin)

  23. Ketone Bodies Acetyl-CoA Keton Bodies - Ketone bodies are formed in the liver from acetyl-CoA - Keton bodies are an important source of energy

  24. Utilization of Ketone Bodies as Energy Source Citric acid cycle (Oxaloacetat) Can be used as energy source (broken down in ATP) -> just if enough Oxaloacetat present !!!

  25. Why do we form Ketone Bodies? • Acetyl-CoA (from β-oxidation) enters citric acid cycle ONLY IF enough oxaloacetate is available • Oxaloacetate is formed (refill of citric acid cycle) by pyruvate (glucolysis) • -> Only if Carbohydrate degradation is balanced -> Acetyl Co-A from β-oxidation enters citric acid cycle !!!! • -> If not balanced -> Keton bodies are formed!!! • Consequence: • Diabetics and if you are on a diet -> oxaloacetate is used to form glucose (gluconeogenesis) -> Acetyl-CoA (from β-oxidation) is converted into Ketone bodies !! • Animals and humans are not able to convert fatty acids -> glucose !!!!! • Plant can do that conversion -> Glyoxylate cycle (Acetyl Co-A -> Oxaloacetate)

  26. Heart muscle uses preferable acetoacetate as energy source The brain prefers glucose, but can adapt to the use of acetoacetate duringstarvation and diabetes. High level of acetoacetate in blood -> decrease rate of lipolysis in adipose tissue.

  27. Diabetes – Insulin Deficiency • Diabetes: • Absence of Insulin -> • Liver cannot absorb Glucose -> cannot provide oxaloacetate to process FA • No inhibition of mobilization of FA from adipose tissue • -> Large amount of Keton bodies produced -> drop in pH -> disturbs function in central nervous system!!!

  28. Fatty Acids are Synthesized and Degraded by Different Pathways Degradation (β-Oxidation) Synthesis • In the mitochondria matrix • Intermediates are linked to CoA • No linkage of the enzymes involved • The oxidants are NAD+ and FAD • Degradation by C2 units -> Acetyl-CoA • In the cytosol • Intermediates are linked to an Acyl carrier protein (ACP) complex • Enzymes are joined in one polypeptide chain -> FA synthase • The reductant is NADPH • Elongation by addition of malonyl ACP + release of CO2 • Synthesis stops at palmitate (C16), additional enzymes necessary for further elongation

  29. Transport of Acetyl-CoA from the Mitochondria-> Cytosol FA synthesis Glycolysis

  30. Activation of Acetyl and Malonyl in Synthesis reactive unit Activation for Synthesis Activation for Degradation

  31. 1st step in Fatty Acid Synthesis – Formation of Malonyl-CoA

  32. Fatty Acid Synthesis

  33. Synthesis by Multifunctional Enzyme Complex in Eukaryotes -> Synthase In animals: a dimer – each 3 domains with 7 activities • Inhibitors: • Antitumor drugs (synthase overexpressed in some breast cancers) • Antiobesity drugs

  34. Fatty Acid Synthesis -> Pathway Integration

  35. Regulation of Fatty Acid Synthesis Acetyl Co-A -------> Malonyl Co-A Carboxylase (key enzyme) Global regulation Local regulation Allosteric stimulation by citrate Glucagon inhibits Insulin activates enzyme

  36. Pathway Integration

  37. Introduction of Double Bonds to Fatty Acids Precursors used to generate longer unsaturated FA Essential FA Mammals cannot introduce double bonds beyond C-9

  38. Desaturation and Elongation of FA Essential FA Mammals cannot introduce double bonds beyond C-9 Eicosanoides -> Hormones

  39. Localization of Lipid Metabolism

  40. Eicosanoides Aspirin + Ibuprofen block enzyme

  41. Aspirin acetylates enzyme Inhibits enzyme by mimicking substrate or intermediate

  42. Eicosanoid Hormones – local hormones Leukotrienes (found in leukocytes): Allergic reaction -> body (immune system) releases chemicals such as histamine and leukotrines -> cause flushing, itching, hives, swelling, wheezing and loss of blood pressure Prostaglandins: stimulate inflammation, regulate blood flow to organs, control ion transport through membranes, induce sleep

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