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Chapter 7

Chapter 7. Biological Oxidation. Biological Oxidation. Loss of electrons loss of e - by one chemical species becomes oxidized gain of e - by another becomes reduced Dehydrogenation oxygenation. 7.1 Principles of Redox Reaction. Redox reaction =reduction/oxidation reaction

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Chapter 7

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  1. Chapter 7 Biological Oxidation

  2. Biological Oxidation • Loss of electrons loss of e- by one chemical species becomes oxidized gain of e- by another becomes reduced • Dehydrogenation • oxygenation

  3. 7.1 Principles of Redox Reaction • Redoxreaction=reduction/oxidation reaction • Flow of e- in redox reactions is responsible (directly or indirectly) for all work done in living organisms. • Electrochemical half cell: the oxidized form and the reduced form of a chemical species. • Two half cell with the common intermediate comprise a coupled redox reation. NADH+H + +(1/2)O2 NAD++H2O

  4. E°(standard electrode potential) is used to measure the affinity for e-of the redox pair. E°= the electrical potential of a half cell compare with a standard hydrogen half cell, the potential of which is zero.

  5. Eº’ (Standard Oxidation-Reduction Potential) is the E°at pH7, 25°C. The standard free energy change ΔGº’ = -n F Δ Eº’

  6. If reaction proceeds in direction X- + H+ X + 1/2 H2 reactions in half cells are H+ + e- 1/2 H and X- X + e- e- flow is from the sample (X/X-) cell to the standard hydrogen half cell, So, reduction potential is -ve. X has a lower affinity for e- than H2 does

  7. If reaction proceeds in direction X + 1/2 H2X- + H+ reactions in half cells are 1/2 H2H+ + e- and X + e-X- e- flow is from the standard reference half cell to the sample (X/X-) cell. So, reduction potential is +ve. X has a higher affinity for e- than H2 does

  8. For the reaction: NADH+(1/2)O2+H+ NAD++H2O Δ Eº’=+1.14V ΔGº’ =-52.6kcal/mol For the synthesis of ATP ADP + Pi + H+ ATP+H2O ΔGº’ =+7.3kcal/mol

  9. Section 7.2 Respiratory Chain and Oxidative Phosphorylation

  10. 7.2.1 Respiratory Chain • Term: A chain in the mitochondria consists of a number of redox carriers for transferring electrons from the substrate to molecular oxygen to form oxygen ion, which combines with protons to form water.

  11. There are 4 protein complexes involved • Complex I: NADH:ubiquinoneoxidoreductase • Complex II: Succinate:ubiquinoneoxidoreductase • Complex III: cytochrome bc1(ubiquinone Cyt coxidoreductase) • Complex IV: cytochrome oxidase

  12. complex Ⅰ NADH→ →CoQ FMN; Fe-SN-1a,b;Fe-SN-4;Fe-SN-3; Fe-SN-2 Complex I (NADH:ubiquinoneoxidoreductase) • Function: transfer electrons from NADH to CoQ • Components: NADH dehydrogenase (FMN) Iron-sulfur proteins (Fe-S)

  13. R=H: NAD+; R=H2PO3:NADP+ NAD(P)+:NicotinamideAdenineDinucleotide (Phosphate)

  14. Oxidation of NADH is a 2-electron, 2-proton reaction NAD+ or NADP+ NADH or NADPH

  15. 2. FMN can transfer 1 or 2 electrons and protons each time FMN: flavin mononucleotide semiquinone = stable free radical fully reduced form

  16. 3. Iron-sulfur clusters (Fe-S) transfers 1-electron each time, without proton involvedFe3++e- Fe2+

  17. 4.Ubiquinone (coenzyme Q, CoQ) is lipid-soluble, not a component of complex Ⅰ,can transfer 1 or 2 electrons and protons each time.Function:transfer electrons and protons from complex Ⅰor complex Ⅱto complex Ⅲ.

  18. Reduced Fe-S NADH+H+ FMN Q NAD+ FMNH2 Oxidized Fe-S QH2 Matrix Intermembrane space

  19. Complex Ⅱ Succinate→ →CoQ Fe-S1;b560;FAD;Fe-S2 ;Fe-S3 Complex II:Succinatedehydrogenase (Succinate: CoQ oxidoreductase) • Function: transfer electrons from succinate to CoQ • Components: Succinatedehydrogenase (FAD, Fe-S) Cytochrome b560

  20. Cytochromes a, b, c are heme proteins, their heme irons participate redox reactions of e- transport.Fe3++e- Fe2+

  21. Intermembrane space Reduced Fe-S Q Succinate FAD fumarate FADH2 Oxidized Fe-S QH2 Matrix Succinate

  22. complex Ⅲ QH2→ →Cyt c b562; b566; Fe-S; c1 Complex III:cytochrome bc1(ubiquinone Cyt coxidoreductase) • Function: transfer electrons from CoQ to cytochrome c • Components: iron-sulfur protein cytochrome b(b562, b566) cytochrome c1

  23. Intermembrane space Matrix Cytochrome c is soluble, which will transfer electrons to complex Ⅳ

  24. 细胞色素C是生物进化最保守的蛋白质之一， 常用来作为系统进行分类的标准。 物种越接近，则细胞色素C的一级结构越相似，其空间构象和功能也相似，其顺序同源性越大

  25. 细胞色素C从线粒体膜间隙释放是多种细胞凋亡的普遍现象细胞色素C从线粒体膜间隙释放是多种细胞凋亡的普遍现象 细胞凋亡又称为细胞程序性死亡，是生物界重要的生命现象之一，是对细胞自身无法修复的损伤的一种有利保护，防止有损伤的细胞进一步增殖而发生病变。与多种疾病如肿瘤、自 身免疫性疾病等的发生发展有关。 通过注射细胞色素C能诱导细胞凋亡，由此可推测通过注射细胞色素C对病灶细胞如癌细胞凋亡加以诱导，可望成为防病治病的一种生物学新疗法

  26. Complex IV Cyt c → → O2 CuA→a→a3→CuB Complex IV:cytochrome oxidase • Function: transfer electrons from Cyt c to molecule oxygen, the final electron acceptor. • Components: cytochrome aa3 copper ion (Cu2+) Cu2+ + e- Cu+

  27. Cytochrome c Coenzyme Q ubiquinone/ol

  28. Sequence of respiratory chain Principles: • e- tend to flow from a redox pair with a lower E°to one with a higher E° • In the e--transport chain, e--carriers are arranged in order of increasing redox potential, making it is possiblethat the gradual release of energy stored in NADH, FADH2

  29. Redox potential redox pair E0

  30. There are two respiratory chains • NADH respiratory chain NADH Complex Ⅰ CoQ Complex Ⅲ cytochrome c Complex Ⅳ O2

  31. Succinate (FADH2) respiratory chain Succinate Complex Ⅱ CoQ Complex Ⅲ cytochrome c Complex Ⅳ O2 Succinate Fumarate

  32. Succinate NADH respiratory chain FADH2 respiratory chain

  33. 7.2.2 Oxidative Phosphorylation • The oxidation of organic nutritions produces the energy-rich molecules： NADH and FADH2. • The oxidation of NADH or FADH2 in mitochondrial is the electron transferring through respiration chain.

  34. The free energy produced in electron transferring supports the phosphorylation of ADP to form ATP. • The oxidation of NADH or FADH2 and the formation of ATP are coupled process, called Oxidation Phosphorylation.

  35. The Chemiosmotic Theory • The free energy of electron transport is conserved by pumping protonsfrom the mitochondrial matrix to the intermembrane space so as tocreate an electrochemical H+ gradient across the inner mitochondrialmembrane. The electrochemical potential of this gradient is the energy recercoir to synthesizeATP. Peter Mitchell

  36. Electrochemical H+ gradient (Proton-motive force) 2 components involved 1. Chemical potential energy due to difference in [H+] in two regions separated by a membrane 2. Electrical potential energy that results from theseparation of charge when a proton moves across the membrane without a electron.

  37. Complex I: 4 H+ expelled pere--pair transferred to Q Complex III: 4 H+ expelled per e--pair transferred to Cyt c Complex IV: 2e- + 2 H+ from matrixconvert ½ O2 to H2O; 2 further H+expelledfrom matrix

  38. Proton pumping:Reduction-dependentconformational switch ofan e--transport complex Conformation 1 (high affinity for H+) Conformation 2 (low affinity for H+).

  39. Inner Membrane Intermembrane space (ab2c9-12) (α3β3γδε) Matrix C ring ATP Synthase

  40. β-subunit take up ADP and Pi to form ATP ADP + Pi ATP Each of 3 b-subunits contains an active site F1: multisubunit complex that catalyzes ATP synthesis F0： proton-conducting transmembrane unit

  41. T L O 3(ADP+Pi) L O T O L T When protons flow back through F0 channel, γ-subunit is rotated by the rotation of c ring, then the conformations of β-subunits are changed, this lead to the synthesis and release of ATP. To form a ATP need 3 protons flow into matrix.

  42. H+ ADP3- ATP4- H2PO4- H+ 胞液侧 F0 基质侧 F1 H2PO4- H+ ADP3- H+ Translocation of ATP , ADP and Pi. ADP3- H2PO4- Intermembrane space Matrix ATP4-

  43. P/O ratios • P/O ratio is the rate of phosphate incorporated into ATP to atoms of O2 utilized. It measure the number of ATP molecules formed per two electrons transfer through the respiratory chain. • NADH respiratory chain : 2.5, • FADH2 respiratory chain: 1.5

  44. During two electrons transfer through NADH respiratory chain, ten protons are pumped out of the matrix. • To synthesis and translocation an ATP, four protons are needed. • So, two electrons transport can result in 2.5 ATP. • To succinate respiratory chain , two electrons transport can result in 1.5 ATP.

  45. Regulation of Oxidative Phosphorylation • 1.PMF (proton motive force) regulate the electron transport. higher PMF lower rate of transport • 2.ADP concentration resting condition: energy demanded is low, ADP concentration is low, the speed of Oxidative Phosphorytion is low. active condition: the speed is high.

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