Fatty Acid Catabolism

1. Fatty Acid Catabolism C483 Spring 2013

2. 1. Which lipid form is transported across the inner mitochondrial membrane before β-oxidation? A) Acylcarnitine. B) Fatty acyl CoA. C) Acetoacetyl CoA. D) Lysophospholipid CoA. 2. There are four steps in the β-oxidation pathway. Some reaction types are listed below. Give the proper reaction types in the order that they occur in the β-oxidation pathway. 1. Condensation 5. hydration 2. Oxidation 6. phosphorylation 3. Reduction 7. rearrangement 4. Thiolysis A) 1, 7, 2, 2 B) 6, 3, 4, 2 C) 1, 2, 3, 4 D) 2, 5, 2, 4

3. 3. The conversion of the laurate CoA (a 12-carbon acylCoA) to carbon dioxide via β-oxidation, the citric acid cycle and oxidative phosphorylation yield approximately ________ ATP equivalents. A) 78 B) 80 C) 82 D) 84 4. A patient is found to have a high concentration of cholesterol in the blood and deposits of cholesterol under the skin. The patient is diagnosed with familial hypercholesterolemia. What is the likely cause of this condition? A) A deficiency in insulin production by the pancreas. B) Insufficient chylomicron concentration in the blood. C) Overproduction of lysosomal lipases. D) Lack of LDL receptors on the surfaces of nonhepatic cells. 5. Ketone bodies form when ______________ is in low concentration: Acetyl CoA Triacylglyceride Cholesterol oxaloacetate

4. Overview • Lipids as a fuel source—diet • Beta oxidation • Mechanism • ATP production • Ketone bodies as fuel

5. TAG and FA • High energy • More reduced • Little water content • 9 Cal/g vs 4 Cal/g for carbs • Unsaturated FA • Glycerol

6. Digestion • Cross from intestine into bloodstream

7. Lipoprotein Metabolism • Liver is the packaging center • VLDL are sent out of liver • Constant cycling of LDL in blood • Genetic cholesterol problem: no LDL receptors in non-liver cells • HDLs are “good cholesterol”

8. Utilization Stage 1:Mobilization Hormone Sensitive Lipase

9. Utilization Stage 2:Transport into Matrix • FA  FA-CoA costs ATP AMP (2 ATP equivalents) • Carnitine ester: high energy bond • Mammals also degrade FA in peroxisome • Major site of regulation of FA degradation

10. Utilization Stage 3: Beta Oxidation • Four step process • Production of • QH2 • NADH • Acetyl CoA

11. Step 1: Acyl CoA Dehydrogenase • Similar to succinate DH from citric acid cycle • Prosthetic FAD/FADH2 • High energy electrons passed on to QH2 • 1.5 ATP

12. Step 2: Enoyl CoA Hydratase • Similar to fumaratehydratase from citric acid cycle • Addition of water • No energy cost/production

13. Step 3: 3-hydroxyacyl CoA DH • Similar to malate DH from citric acid cycle • Oxidation of secondary alcohol to ketone • NADH production • 2.5 ATP

14. Step 4: Thiolase • CoA is used as a nucleophile in a “nucleophilic acyl substitution” • FA shortened by 2 carbons • Acetyl CoA produced • 10 ATP through CAC

15. ATP Accounting • How much ATP is netted from palmitate (16 carbons)? • Cost 2 ATP to activate to palmitate CoA • Run through beta oxidation SEVEN times • 7 QH2 = 10.5 ATP • 7NADH = 17.5 ATP • 8 acetyl CoA produced = 80 ATP • Total: 106 ATP, or 6.625 ATP per carbon • Compare to glucose, which is 5.33 ATP per C

16. Processing Other FA • Unsaturated and trans fatty acids • Enzymes can handle processing • Produce 1.5 ATP less per unsaturation (why?) • Odd chain fatty acids • Rare, but do occur in diet • One of 2 requirements for Vitamin B12 (cobalamine) in human diet

17. Alternate Fate of Acetyl CoA • Fasting, Diabetes • Glycolysis is down, gluconeogenesis is up • Oxaloacetate depleted • Citric acid cycle has diminished capacity • Acetyl CoA levels build up • Ketone bodies are formed

18. Ketone Bodies • Water soluble form of lipids • Less potential energy than FA • Main energy source of brain in starvation • Also used in muscle and intestine

19. Regulation

20. Answers • A • D • B • D • D