Chapter 19 Oxidative Phosphorylation and Photophosphorylation Part I) Electron Transport

1. Chapter 19 Oxidative Phosphorylation and Photophosphorylation Part I) Electron Transport

2. From Garrett & Grisham

3. Electrons transferred via NADPH Electrons transferred via NADPH

4. {80% proteins} {30-40% lipids & 60-70% proteins} Provide inner membrane with large surface area Intermembrane space • Outer Membrane • Contains porin • Allows free diffusion of molecules • with molecular weight less than • 10,000 Porins are transmembrane channels for small molecules • Inner Membrane • Impermeable to molecules & ions

5. Matrix • contains all of TCA cycle enzymes {except, succinate dehydrogenase which is located in the inner membrane} • contains circular DNA, ribosomes and enzymes required to synthesize proteins encoded within the mitochondrial genome From Lehninger Principles of Biochemistry

6. Separation of functional complexes of the respiratory chain Components of the electron transport chain can be purified from the mitochondrial inner membrane From Lehninger Principles of Biochemistry

7. Electron Transport Link between glycolysis, TCA cycle, fatty acid oxidation and electron transport chain Direct link between TCA cycle and electron transport chain • e- carried by reduced coenzymes are passed through a chain of proteins and coenzymes to drive the generation of a proton gradient across the inner mitochondrial membrane

8. 2 other ways to feed electrons into ubiquinone

9. From Lehninger Principles of Biochemistry

10. Electron transfer from NADH to O2 involves multi-subunit inner membrane complexes I, III, & IV, plus coenzyme Q and cytochrome c. Within each complex, electrons pass sequentially through a series of electron carriers.

11. The electron transport chain NADH FADH2 Fe.S FMN Fe.S Q Cyt b Fe.S Cyt c1 Free Energy Relative to O2 (kcal / mol) Cyt c Cyt a Cyt a3 O2 NADH (reductant) + H+ + ½ O2 (oxidant) NAD+ + H2O Electrons generally fall in energy through the chain - from complexes I and II to complex IV

12. Redox reactions are among a cell's most important enzyme-catalyzed reactions. Oxidation and reduction refer to the transfer of one or more electrons from a donor to an acceptor, generally of another chemical species. The donor is oxidized, the acceptor reduced.

13. Oxidative Phosphorylation The proton gradient runs downhill to drive the synthesis of ATP

14. Electron Carriers: NAD+/NADH and FAD/FADH2 were introduced earlier • FMN (Flavin Mono Nucleotide) is a prosthetic group of some flavoproteins{It is similar in structure to FAD, but lacks the adenine nucleotide} • In solution FMN (like FAD) can accept 2 e- + 2 H+ to yield FMNH2 • When bound at the active site of some enzymes, FMN can accept 1 e-, converting it to the half-reduced semiquinone radical. The semiquinone can accept a second e- to yield FMNH2

16. Prosthetic groups of cytochromes • Heme  is a prosthetic group of cytochromes • Mitochondria has 3 classes of cytochromes, designated a, b, and c Found in Hb The heme iron atom can undergo a 1 electron transition between ferric and ferrous states:       Fe3+ + e- <--> Fe2+ From Lehninger Principles of Biochemistry

17. Structure of mitochondrial cytochrome c Heme is covalently linked to the protein via S atoms From Garrett & Grisham

18. Iron-sulfur centers (Fe-S) • - electron transfer proteins may contain multiple iron-sulfur centers. • transfer only one electron even if they contain two or more iron atoms, because of the close proximity of the iron atoms.  • a 4-Fe center might cycle between the redox states: Fe3+3, Fe2+1 (oxidized) + 1 e-<-->Fe3+2, Fe2+2( reduced)

19. Iron-sulfur centers From Lehninger Principles of Biochemistry

20. Ferredoxin of the cyanobacterium Anabaena 7120 2Fe-2S center Fe S From Lehninger Principles of Biochemistry

21. Protein bound copper, a one-electron transfer site, which converts between Cu+ and Cu2+

22. Ubiquinone (Q or coenzyme Q) From Lehninger Principles of Biochemistry

23. A lipid soluble coenzyme (UQ) shuttle between protein complexes Hydrophobic tail allows it to diffuse freely in the hydrophobic core of the inner mitochiondrial membrane Mobile electron carrier

24. Complex I

25. NADH dehydrogenase aka NADH-Coenzyme Q reductase o NADH 2e- donor FMN 1 or 2 e- donor Fe-S clusters 1 e- donor • Estimated mass of this complex 850 kD • Involves more than 30 polypeptide chains • One molecule of FMN • As many as 7 Fe-S clusters (2Fe-2S & 4Fe-4S) • Precise mechanism of this complex is unknown From Lehninger Principles of Biochemistry

26. Complex I o r o r o r o

27. Inhibitors of complex I • Rotenone is a common insecticide that inhibits complex I • Rotenone is obtained from the roots of several species of plants • Rats exposed to rotenone over a period of weeks develop symptoms of Parkinson’s disease • Appear to inhibits reduction of Q and the oxidation of Fe-S clusters of complex I {Painkiller Demerol also exert inhibitory actions on this complex}

28. Inhibitors of Complex I

29. Complex II

30. Complex II H+ transport does not occur in this complex Succinate-CoQ Reductase aka Succinate dehydrogenase (from TCA cycle!) o • Succinate • Fumarate r r FAD Succinate dehydrogenase o FADH2 r o • Mass of 100 – 140 kD • Composed of 4 subunits, including 2 Fe-S proteins • Three types of Fe-S cluster: 4Fe-4S, 3Fe-4S, 2Fe-2S • Path: Succinate FADH2 2Fe2+ UQH2

31. Inhibitors of complex II 2-Thenoyltrifluoroacetone & carboxin block complex II Inhibitors of complex II

32. Electron Transport From Lehninger Principles of Biochemistry