Title: Fatty Acid Metabolism
1Fatty Acid Metabolism
2Free Energy of Oxidation of Carbon Compounds
3Metabolic Motifs
4Naming 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
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6Fatty Acid Metabolism
- Triacylglycerols are concentrated energy stores
- Utilization of FAs in 3 stages of processing
(TAG -gt 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
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8Utilization of Fatty Acids requires 3 Stages of
Processing
- Lipids (Triacylglycerols) are mobilizes -gt broken
down to fatty acids glycerol - Fatty acids activated and transported into
mitochondria - Fatty acids are broken down to acetyl-CoA -gt
citric acid cycle
9Dietary Lipids are Broken Down by Pancreatic
Lipase and Transported through the Lymph System
10Dietary Lipids are Broken Down by Pancreatic
Lipase and Transported through the Lymph System
Packed together with Apoprotein B-48 -gtto give
Chylomicrons (180-500 nm in diameter)
11Mobilisation of Triacylglycerols That are Stored
in Adipocyte Cells
Lipolysis inducing hormones Epinephrine,
glucagon (low blood glucose level),
adrenocorticotropic homones -gt Insulin inhibits
lipolysis Protein Kinase A phosphorylates
(activates) -gt Perilipin HS lipase Perilipin
(fat droplet associated protein) -gt restructures
fat to make it more accessible for lipase Free
fatty acids and glycerol are released into the
blood stream -gt bound by serum albumin -gt serves
as carrier in blood
Muscle cells
12Glycerol can be converted to Pyruvate or Glucose
in the Liver !!! Conversion of Glucose -gt
Glycerol possible !!!
Intermediates in Glycolysis ands Glyconeogensesis
Convertion of Glucose -gt Acetyl-CoA -gt Fatty
acid -gt Fat possible !!! Convertion of Fat -gt
fatty acids -gt Acety-CoA -gt Glucose impossible !!!
131. Fatty Acid Activation - Fatty Acid Degradation
142. Transport of Fatty Acids into the Mitochondria
Symptoms for deficiency of carnitine mild
muscle cramping -gt weakness -gt death
15Fatty Acid Oxidation (ß-Oxidation Pathway) in the
Mitochondria
- 4 Steps in one round
- Oxidation -gt introduction of double bond between
a-ß carbon, generation of FADH2 - Hydration of double bound
- Oxidation of hydroxy (OH) group in ß- position,
generation of NADH - Thiolysis -gt cleavage of 2 C units (acetyl CoA)
Other oxidations -gt ?-Oxidation in the
endoplasmatic rediculum of liver and kidney
many C-10 to C-12 carbons,
normally not the main
oxidation pathway -gt if problems with
ß-oxidation -gt a-Oxidation in peroxisomes on
branched FA (branch on ß-carbon)
16Fatty Acid Oxidation (ß-Oxidation Pathway) in the
Mitochondria
- Acyl CoA Dehydrogenase
- chain-length specific
- FA with C-12 to C-18 -gt long-chain isozyme
- FA with C-14 to C-4 -gt medium-chain isozyme
- FA with C-4 and C-6 -gt short-chain isozyme
17First 3 Rounds in Degradation of Palmitate (C-16)
Complete oxidation of Palmitate -gt 106
ATP Complete oxidation of Glucose -gt 30 ATP
18Fatty Acid Oxidation in Peroxisomes
Peroxisome in liver cell
Fatty acid oxidation stops at Octanyl-CoA (C-8)
-gt may serve to shorten long chain to make them
better suitable for ß-Oxidation in
mitochondria In Peroxisomes Flavoprotein Acyl
CoA dehydrogenase transfers electrons (not FADH2)
19Fatty Acid Oxidation in Peroxisomes
Catalase
regeneration in cytosol
Acetyl-CoA produced in the peroxisomes -gt used as
precursors and not for energy consumption
20Enzymes of ß-oxidation
21Oxidation of Monounsaturated FA and FA with
odd-numbered double bonds
22Oxidation of Polyunsaturated Fatty Acids
- 1 acetyl CoA
23Oxidation of Odd-Chain Fatty Acids -gt Propionyl
CoA
In lipids from many plants and marine organisms
Reaction requires Vitamin B12 (Cobalamin)
Citric acid cycle
24Oxidation of Odd-Chain Fatty Acids -gt Propionyl
CoA
Vitamin B12 Animals and plants cannot produce
B12 -gt produced by a few species of bacteria
living in the intestine Deficiency-gt failure to
absorb vitamine (not enough of the protein that
facilitates uptake) -gt reduced red blood cells,
reduced level of hemoglobin, impairment of
central nervous system
Reaction requires Vitamin B12 (Cobalamin)
25Ketone Bodies
Acetyl-CoA
Keton Bodies
- Ketone bodies are formed in the liver from
acetyl-CoA - Keton bodies are an important source
of energy
26Utilization of Ketone Bodies as Energy Source
Citric acid cycle (Oxaloacetat)
Can be used as energy source (broken down in ATP)
-gt just if enough Oxaloacetat present !!!
27Why do we form Ketone Bodies?
- Acetyl-CoA (from ß-oxidation) enters citric acid
cycle ONLY IF enough oxaloacetate is available - Oxaloacetate is formed (refill of citric acid
cycle) by pyruvate (glucolysis) - -gt Only if Carbohydrate degradation is balanced
-gt Acetyl Co-A from ß-oxidation enters citric
acid cycle !!!! - -gt If not balanced -gt Keton bodies are formed!!!
- Consequence
- Diabetics and if you are on a diet -gt
oxaloacetate is used to form glucose
(gluconeogenesis) -gt Acetyl-CoA (from
ß-oxidation) is converted into Ketone bodies !! - Animals and humans are not able to convert fatty
acids -gt glucose !!!!! - Plant can do that conversion -gt Glyoxylate cycle
(Acetyl Co-A -gt Oxaloacetate)
28Heart muscle uses preferable acetoacetate as
energy source The brain prefers glucose, but can
adapt to the use of acetoacetate during
starvation and diabetes. High level of
acetoacetate in blood -gt decrease rate of
lipolysis in adipose tissue.
29Diabetes Insulin Deficiency
- Diabetes
- Absence of Insulin -gt
- Liver cannot absorb Glucose -gt cannot provide
oxaloacetate to process FA - No inhibition of mobilization of FA from adipose
tissue - -gt Large amount of Keton bodies produced -gt
drop in pH -gt disturbs function in central
nervous system!!!
30Fatty Acids are Synthesized and Degraded by
Different Pathways
Degradation (ß-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 -gt Acetyl-CoA
- In the cytosol
- Intermediates are linked to an Acyl carrier
protein (ACP) complex - Enzymes are joined in one polypeptide chain -gt 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
31Transport of Acetyl-CoA from the Mitochondria-gt
Cytosol
FA synthesis
Glycolysis
32Activation of Acetyl and Malonyl in Synthesis
reactive unit
Activation for Synthesis
Activation for Degradation
331st step in Fatty Acid Synthesis Formation of
Malonyl-CoA
34Fatty Acid Synthesis
35Synthesis by Multifunctional Enzyme Complex in
Eukaryotes -gt Synthase
In animals a dimer each 3 domains with 7
activities
- Inhibitors
- Antitumor drugs (synthase overexpressed in some
breast cancers) - Antiobesity drugs
36Fatty Acid Synthesis -gt Pathway Integration
37Regulation of Fatty Acid Synthesis
Acetyl Co-A -------gt Malonyl Co-A
Carboxylase (key enzyme)
Global regulation
Local regulation
Allosteric stimulation by citrate
Glucagon inhibits
Insulin activates enzyme
38Pathway Integration
39Introduction of Double Bonds to Fatty Acids
Precursors used to generate longer unsaturated FA
Essential FA Mammals cannot introduce double
bonds beyond C-9
40Desaturation and Elongation of FA
Essential FA Mammals cannot introduce double
bonds beyond C-9
Eicosanoides -gt Hormones
41Localization of Lipid Metabolism
42Eicosanoides
Aspirin Ibuprofen block enzyme
43Aspirin acetylates enzyme
Inhibits enzyme by mimicking substrate or
intermediate
44Eicosanoid Hormones local hormones
Leukotrienes (found in leukocytes) Allergic
reaction -gt body (immune system) releases
chemicals such as histamine and leukotrines -gt
cause flushing, itching, hives, swelling,
wheezing and loss of blood pressure Prostaglandin
s stimulate inflammation, regulate blood flow to
organs, control ion transport through membranes,
induce sleep