Chapter 3 Metabolisms of Carbohydrates

1. Chapter 3 Metabolisms of Carbohydrates 3. Aerobic catalysis of carbohydrate and tricarboxylic acid cycle 糖的有氧分解与三羧酸循环 3.1 A survey of introduction 概述

2. 三羧酸循环（ Tricarboxylic acid cycle) TCA Cycle TAC • Kreb’s循环（ Kreb’s cycle) • 柠檬酸循环（Citric cycle)

3. 3.1.1 葡萄糖的有氧分解包括三个部分： Glycolysis Ⅰ Glucose Pyruvate Acetal-CoA TCA Cycle Yielding of acetyl-CoA NAD+ CoA-SH Ⅱ CO2 NADH +H+ acetyl-CoA is oxidized Ⅲ CO2 + H2O

4. 3.1.2 三羧酸循环的研究简史 • Krebs提出三羧酸循环的观察与推理 1. 肌肉悬液可以氧化二羧酸:succcitate, fumarate, maltate, oxaloacetate, -ketoglutarate和三羧酸：citrate, isocitrate, aconitrate; 2. 以上二羧酸和三羧酸促进糖和pyruvate的氧化; 3. 丙二酸（malonate）抑制pyruvate 的氧化； 4. Oxaloacetate + pyruvate citrate 5. 在丙二酸存在下，加入fumarate, maltate, oxaloacetate可引起succcitate积累；

5. 3.1.2 三羧酸循环的研究简史 6. 在丙二酸存在下，加入oxaloacetate可克服抑制，并且每消耗1分子 pyruvate, 就消耗1分子oxaloacetate； 7. 循环中每一酶促反应的速度与pyruvate以及O2的利用速度是一致的。

7. 3.2 Pyruvate is oxidized to acetyl-CoA • Pyruvate is transported into mitochondria then oxidized to acetyl-CoA (releasing CO2) before entering the citric acid cycle NAD+ NADH +H+ Pyruvate Acetal-CoA + CO2 pyruvate dehydrogenase complex

8. 3.2.1 pyruvate dehydrogenase complex pyruvate dehydrogenase (E1) dihydrolipoyl transacetylase (E2) three enzymes dihydrolipoyl dehydrogenase (E3) complex CoA-SH NAD+/NADH•H+ Lipoate (硫辛酸） FAD TPP Mg2+ six coenzymes Protein kinase Phosphate protein phosphatase Regular proteins

9. 丙酮酸dHE复合物的组成 20 60 5-6

10. 3.2.2 The process of oxidation from Pyruvate to acetyl-CoA

12. 活性乙醛

14. : Ө E2 E2 dihydrolipoyl transacetylase + Ө E2

15. E3 E3

17. E3 E3

18. 3.2.3 Regulation of pyruvate dehydrogenase complex • 受蛋白激酶和磷酸蛋白磷酸酶控制――磷酸化失活 • 受激素调节 • 受能荷效应物调节 ADP, AMP E1 激活剂 CoASH, NAD+ E2, E3 ATP, GTP E1 抑制剂 Acetal-CoA NADH•H+ E2, E3

19. 3.3 Tricarboxylic Acid Cycle • 3.3.1 Reaction process of tricarboxylic acid cycle

21. NAD+ and FAD takes the electrons during acetyl-CoA oxidation • Each acetyl-CoA is completely oxidized to two CO2, generating three NADH, one FADH2, and one GTP; • The metabolites contain six, five or four carbons in the cycle.

22. 3.3.1.1 The cycle begins with the condensation of acetyle-CoA and oxaloacetate to form citrate 草酰乙酸 Catalyzed bycitrate synthase(a dimer)

23. 柠檬酸合酶 (Citric acid synthase) • 催化TCA的第一步反应，反应先生成柠檬酰CoA，再水解为柠檬酸，是放能反应，不可逆。是TCA的第一个调节酶，活性受ATP、NADH、Succinyl CoA及长链脂酰CoA的抑制，对于TCA是一个rate-limitting step。 • 氟乙酰CoA在酶的作用下可与草酰乙酸生成氟柠檬酸，顺乌头酸酶只识别柠檬酸，对氟柠檬酸没有作用，致使TCA中断，这种合成为致死合成(lethal synthesis)。在代谢研究的应用上，曾被广泛用于杀虫剂或灭鼠药的生产。(现已被明令禁止)

24. 合酶 (synthase)： • 催化加合反应，促使合成 • 合成酶 (synthetase)： • 催化连接反应，一般需要NTP

25. 3.3.1.2 Citrate isomerizes to isocitrate via cis-aconitate * * * * * * 90% 4% 6% G0’ = -2.1 kJ/mol G0’ = 8.4 kJ/mol Floride citrate is the special inhbitor of aconitase

26. 柠檬酸投影式 pro-S pro-R S: sinister R: rectus 前手性、潜手性（pro-chiral)

28. Aconitase catalysing a stereo reaction * *

29. * *

30. * *

31. * *

33. Aconitase catalysing a stereo reaction isocitrate citrate isocitratecitrate

34. Specificity of stereochmistry of actonitase: • Actonitase can distinguish between citrite’s pro-R and pro-S carboxymethyl groups; • Actonitase catalyzes the stereospecific trans addition of OH- and H+ across the double bond.

35. 3.3.1.3 Isocitrate undergoes oxidative decarboxylation to form a-ketoglutarate * * * * Reaction 4 and 5 Go’ = -20.9 kJ/mol

36. * * * * * * CO2 O for isocitrate dehydrogenase Positive effectors: ADP, AMP, isocitrate Negative effectors: ATP, NADH

37. 3.3.1.4-ketoglutarate undergoes oxidative decarboyxlation to form succinyl-CoA * * * * Catalyzed by -ketoglutarate dehydrogenase complex; almost the same as pyruvate dehydrogenase complex; E3 is identical, E1 and E2 are very similar.

38. 3.3.1.5 Cleavage of the thioester bond in succinyl-CoA is coupled to GTP or ATP formation * * （也称琥珀酸硫激酶）

39. 3.3.1.6 Succinate is oxidized to fumarate 琥珀酸 延胡索酸 1. The enzyme catalyzes stereospecific dehydrogenation 2. Malonate is the inhibitor of the reaction

40. 丙二酸 琥珀酸

41. 3.3.1.7 Fumarate is hydrated to L-malate 苹果酸 延胡索酸

42. 3.3.1.8 Oxaloacetate is regenerated by the oxidation of L-malate * * or * *

43. Details worked out by studying highly purified enzymes of the cycle in vitro; 使用高度提纯的酶在体外实验证明了这一代谢途径 Also by isotope tracer experiments in vivo; 通过体内同位素示踪法也证明了这一代谢途径 The citric acid cycle was confirmed to be universal in cellsTCA循环被证明在细胞中是广泛存在的

44. 3.3.2Survey of TCA cycle O • 1. 总反应式: CH3-C-SCoA + 3NAD+ + FAD + GDP + Pi + 2H2O 2CO2 + 3NADH•H+ + FADH2 + GTP + CoA-SH • 2. There are two carbon atoms in the form ofacetyl-SCoA enters every cycle; and there are two decarboxylations take place in each cycle; • 乙酰辅酶A中的二碳乙酰基进入TCA循环；在循环中发生两次脱羧反应

45. 3.3.2Survey of TCA cycle 3. There are four dehydrogenation reactions take place in each cycle; 在循环中发生四次脱氢反应 • 4. There is a substrate level phosphoralation; • 循环中发生一次底物水平磷酸化

46. 3.3.2 Survey of TCA cycle • 5. The reactions catalyzed by aconitase and fumarase is asymmetry reactions; 顺乌头酸酶和延胡索酸酶等催化非对称反应 • 6. All of the intermediary metabolisms are not synthesis and decomposition netly. 所有的中间代谢产物在代谢中没有净合成或净降解

47. 3.4The energetics of the areable decomposotion of glucose葡萄糖有氧分解途径的能量计算 • 1. Acetyl in acetyl-SCoA was oxydized: 化学氧化释放的自由能：874.9 kJ/mol 生物氧化释放的自由能：520.9 kJ/mol 用于ATP合成的自由能：354 kJ/mol

48. The energetics of the aerobic decomposotion of glucose • 2. Hydrations in TCA-cycle: H2O The third H2O entered in TCA cycle: GDP + Pi = GTP + H2O succinyl-CoA + H2O H2O Succidate + CoA-SH

49. The energetics of the aerobic decomposotion of glucose • 3. Dehydrogenations in oxydation of glucose: In EMP: C6H12O6 2×pyruvate + 4H In formation of acetyl-CoA: 2×pyruvate 2 × CoA-SH 2×acetyl-CoA + 4H +2CO2 In TCA cycle: 2×acetyl-CoA + 2× 3 H2O 16H + 4CO2 2 × CoA-SH So: C6H12O6 + 6H2O 24H + 6 CO2 6O212H2O C6H12O6 + 6O2 6H2O + 6 CO2

50. The energetics of the aerobic decomposotion of glucose • 4. Caculation of energy Numbers of ATP ATP 4 - 2 In EMP: (→FADH2) 2NADH•H+ 2 × 3 (2 × 2 ) In formation of acetyl-CoA: 2NADH•H+ 2 × 3 3NADH•H+ × 2 3 × 3 × 2 In TCA cycle: FADH2 × 2 1 × 2 × 2 GTP × 2 1 × 1 × 2 Summery: 38 (36)