Metabolism of lipids

1. Metabolism of lipids

2. Course Content Digestion and absorption of lipids Triacylglycerol metabolism Phospholipid metabolism Cholesterol metabolism plasma lipoprotein metabolism

3. Summary fats : triacylglycerols, TG cholesterol, Ch lipids Definition Classes cholesteryl ester, CE lipoids phospholipids, PL glucolipids, GL • Function

4. nomenclature Fatty acids： Saturated fatty acids 14〜20C palmitic acid 16C stearic acid 18C Unsaturated fatty acids Linolenic acid 18C three unsaturated bonds Linoleate 18C two unsaturated bonds Arachidonic acid 20C four unsaturated bonds Essential fatty acids required for the growth of mammals and they must be obtained from food. Including linoleate、linolenate, arachidonic acid amount unsaturated in plant

6. Section I Digestion and absorption of lipids • digestion： • small intestine：bile、pancreatic lipase、colipase、phospholipase A2、cholesteryl esterase • product：2-monoacylglycerol(MG)、FFA、Cholesterol、lysophospholipid • absorption

10. Chemical Structure of Triacylglycerol

11. Fatty Acid Synthesis • Palmitic acid synthesis • Elongation of FA carbon-chainER • ER --Mitochondrial • Synthesis of Unsaturated FA • Regulation of unsaturated FA

12. Biosynthesis ofpalmitic Acid • Tissues：liver(major site) 、kidney、 breast、adipose、 lung 、 brain ---Cytosol • Materials：Acetyl-CoA、NADPH+H+、ATP、HCO3- and Mn2+ • Pathway ---Synthesis of malonyl-CoA ---Synthesis of fatty acid

13. Citrate Pyruvate Cycle

14. malonyl-CoA Synthesis 限速酶

16. The overall reaction, which is spontaneous, may be summarized as: HCO3- +ATP+ acetyl-CoAADP+ Pi + malonyl-CoA

17. Acetyl-CoA Carboxylase, which converts acetyl-CoA to malonyl-CoA, is the committed step of the fatty acid synthesis pathway. The mammalian enzyme is regulated, by • phosphorylation • allosteric control by local metabolites. Conformational changes associated with regulation: • In the active conformation, Acetyl-CoA Carboxylase associates to form multimeric filamentous complexes. • Transition to the inactive conformation is associated with dissociation to yield the monomeric form of the enzyme (protomer).

18. AMP-Activated Kinase catalyzes phosphorylation of Acetyl-CoA Carboxylase, causing inhibition. The decreased production of malonyl-CoA prevents energy-utilizing fatty acid synthesis when cellular energy stores are depleted. (AMP is abundant only when ATP has been extensively dephosphorylated.)

19. The antagonistic effect of insulin, produced when blood glucose is high, is attributed to activation of Protein Phosphatase.

20. Palmitoyl-CoA (product of Fatty Acid Synthase) promotes the inactive conformation, diminishing production of malonyl-CoA, the precursor of fatty acid synthesis. This is an example of feedback inhibition. Regulation of Acetyl-CoA Carboxylase by local metabolites:

21. [Citrate] is high when there is adequate acetyl-CoA entering Krebs Cycle. Excess acetyl-CoA is then converted via malonyl-CoA to fatty acids for storage. Citrate allosterically activates Acetyl-CoA Carboxylase.

22. Fatty acid synthesis from acetyl-CoA & malonyl-CoA occurs by a series of reactions that are: • in bacteria catalyzed by 6 different enzymes plus a separate acyl carrier protein (ACP) • in mammals catalyzed by individual domains of a very large polypeptide that includes an ACP domain. NADPH serves as electron donor in the two reactions involving substrate reduction. The NADPH is produced mainly by the Pentose Phosphate Pathway.

23. Mammalian fatty acid synthase • A dimer of two polypeptides of 240 kDa each • Each polypeptide contains eight domains that represent the seven catalytic centres plus an integral acyl carrier protein (ACP) domain

24. 4′ phosphopantetheine

25. The structure of the mammalian Fatty Acid Synthase protein is summarized aboveKS = b-Ketoacyl Synthase (Condensing Enzyme)---(Cys)AT =Acyl transferaseMT = Malonyl/Acetyl-CoA Transacylase DH = DehydrataseER = Enoyl Reductase KR = b-Ketoacyl Reductase TE = ThioesteraseACP = Acyl Carrier Protein ---(Pant)

26. 4. Reduction 5. Acyl transfer 3.Dehydration 1.Condensation 2.Reduction

27. Elongation of FA Carbon-chain • ER • Mitochondria • Synthesis of unsaturated FA • unsaturated FA ：软油酸、Oleate、linoleate、linolenate、arachidonic acid （ Essential FA） • Essential FA：required for the growth of mammals and they must be obtained from food. Including linoleate、linolenate, arachidonic acid

28. Regulation of FA synthesis • Dietary factors: carbohydrate promotes synthesis • Hormone factors insulin，“store hormone”，increase FA synthesis Glucagon ，“release hormon”，inhibit FA synthesis

29. Important of polyunsaturated fatty acids---prostaglandins (PG)、 thromboxanes (TX)、 leukotrienes (LT) • Chemical structure and nomenclature of PG、 TX、 LT • Synthesis of PG、TX and LT • Physiological functions of PG、TX and LT

32. Thromboxane A2 Leukotriene A4(LTA4)

33. Synthesis of Triglycerideslocation：liver、adipose tissue and small intestinal materials：glucose、dietary fatspathway：Acylglycerol pathwaydiacylglycerol pathway

35. Degradation of Triacylglycerols • Lipolysis • Glycerol Metabolism • β-Oxidation • Other oxydation modes of fatty acid • Formation and utilization of Ketone Bodies

36. Lipolysis • Concept • Committed enzyme：hormone-sensitive triglyceride lipase (HSL) • Lipolysis hormones：adrenalin 、glucagon、ACTH and TSH • Anti-lipolysis hormones：Insulin、PEGE2 and Nicotinic Acid

37. PPi ADP HSL (inactive) HSL (active) Pi P

38. Glycerol metabolism

39. Experimental evidence for β-Oxidation of fatty acid

40. β-Oxidation of fatty acid • 概念：脂肪酸氧化从羧基端β-碳原子开始，每次释放出一个二碳片段（acetyl-CoA） • Steps：Activation of FAenter into mitochondria β-oxidation TAC(Tricarboxylic acid cycle)

42. Activation of fatty acid —Formation of Acyl-CoA • Location：cytosol acyl-CoA

43. Carnitine (Acyl-CoA) (Carnitine)

44. Mitochondrion

45. Carnitine acyltransferase Ⅰ 限速酶 CoASH Carnitine acyltransferase Ⅱ CoASH

46. β-Oxidation of fatty acid • location：mitochondrial matrix • 过程：在脂肪酸β-氧化多酶复合体的催化下，从脂酰基β碳原子开始，dehydrogenation、加水hydration、dehydrogenation、thiolysis四步，生成一分子比原来少两个碳原子的脂酰CoA(acyl-CoA)及一分子乙酰CoA(acetyl-CoA)

47. β α FAD (dehydrogenation) FADH H2O (hydration) NAD+ (dehydrogenation) H+ NADH CoASH (thiolysis)

48. (dehydrogenation) (hydration) (dehydrogenation) (thiolysis)

49. 脂肪酸β-Oxidation要点 • 脂肪酸仅需活化一次（cytosol），消耗一个ATP的两个高能键； • Acyl-CoA由carnitine运入线粒体，限速酶：CAT-Ⅰ； • β-Oxidation（mitochondrion）: including dehydrogenation、hydration、dehydrogenation、thiolysis four repeated steps

50. 脂肪酸氧化的能量生成 • 如软脂酸（C16）： • 7次β-氧化，生成8分子乙酰CoA、7分子FADH2及7分子NADH 即 12 ×8 +2×7+3 ×7=131分子ATP • 脂肪酸活化时消耗2个高能磷酸键 • 净生成131-2=129分子ATP • formula：12 × +5 ×( -1) –2 • 能量利用率：