Chapter 6 Biological Oxidation

1. Chapter 6Biological Oxidation The biochemistry and molecular biology department of CMU

2. Biological oxidation is the process in which substances (carbohydrate, Lipid, AAs) are oxidized in living organism.

3. Oxidation types: Dehydrogenation Electron lost Oxygenation

4. Nature of biological oxidation： 1. 37℃, pH 7.4, enzymatic reaction. 2. Energy released gradually. 3. Formation of H2O. 4. Formation of CO2 by decarboxylation.

5. General situation of biological oxidation

6. §1 Respiratory Chain §2 Oxidative Phosphorylation §3 ATP §4 Shuttle Systems

7. § 1 Respiratory Chain

8. A chain in the mitochondria consists of a number of redox carriers for transferring hydrogens removed from the substrate to oxygen to form water. The chain is termed a respiratory chain, also called electron transport chain (ETC).

9. Composition of Respiratory Chain Complexes

10. Position of Respiratory Chain Complexes

11. Order of Respiratory Chain Complexes

12. Composition of ETC Hydrogen carrier：NAD + FMN FAD CoQ electron carrier：Fe-S Cyt

13. 1. Nicotinamide coenzymes • NAD+/NADH (Nicotinamide Adenine Dinucleotide, CoⅠ) • NADP+/NADPH(Nicotinamide Adenine Dinucleotide Phosphate, CoⅡ) The nicotinamide is the vitamin PP.

14. NAD+

15. NADP+

17. 2. Flavin prosthetic groups FMN: FlavinMononucleotide FAD: Flavin Adenine Dinucleotide They contain the riboflavin (Vit B2).

18. FMN Isoalloxazine ribitol

19. FAD

22. NAD+ is a coenzyme, that reversibly binds to enzymes. • FAD is a prosthetic group, that remains tightly bound at the active site of an enzyme.

23. 3. Fe-S Iron-sulfur centers (Iron-sulfur protein,Fe-S) are prosthetic groups containing 2, 3, 4 or 8 nonheme iron atoms complexed to elemental and cysteine S.

24. Iron-sulfur centers

25. 2 Fe iron-sulfur center of ferredoxin. 2 Fe colored orange; elemental & Cys S yellow.

26. Different types of iron-sulfur centers

27. Iron-sulfur centers transfer only oneelectron. Fe3+ + e- Fe2+

28. 4. CoQ Coenzyme Q (CoQ, ubiquinone) is very hydrophobic. It dissolves in the membrane. Coenzyme Q functions as a mobile e- carrier within the mitochondrial inner membrane.

31. 5. Cytochromes Cytochromes (Cyt)are proteins with heme prosthetic groups. They absorb light at characteristic wavelengths. • Hemes in the 3 classes of cytochrome (a, b, c) differ slightly in substituents on the porphyrin ring system.

32. Hemes a & a3 are often referred to as cytochromes aa3. • Cytochrome c is a small, water-soluble protein with a single heme group.

33. Heme b

34. Heme c

35. Heme c

37. Heme a

38. The heme iron can undergo an electron transition between ferric and ferrous states: Fe3+ + e- Fe2+

39. The sequence of the components in the respiratory chain has been deduced in several ways. 1. Inhibitor. 2. O2 issuddenly introduced into the system. 3. Standard redox potential.

40. Inhibitor

41. Standard reduction potentials for respiratory chain and related electron carriers

42. NADHrespiratorychain： • Succinaterespiratorychain：

44. §2 Oxidative Phosphorylation

45. Oxidative phosphorylation: The phosphorylation of ADP to ATP coupled to electron transfer from a substrate to molecular oxygen.

46. Substrate level phosphorylation： Phosphorylation of ADP or GDP to ATP or GTP coupled to the dehydrogenation of an organic substrate.

47. Coupled site: • P/O ratio is the number of inorganic phosphates incorporated into ATP per oxygen atom consumed. (number of ATP / 2H)

48. P/O ratio of some substrate

49. succinate -hydroxybutyrate Vit C E0' ∆E0' ∆G0'

50. Three Coupled sites ① NADH → CoQ ② CoQ → Cyt c ③ Cyt aa3→ O2