Components of Electron Transport System

Lesson 31 : Biochemical energetics and biological oxidation

Components of Electron Transport System

There are 5 protein complexes:

  1. NADH-ubiquinone oxidoreductase
  2. Transfers 2e- from NADH to Q as hydride ion (H-)

    First electron transferred to FMN --> FMNH2 ---> Fe-S cluster ---> Q

    Also pumps 4H+/2e- into intermembrane space

  3. Succinate-ubiquinone oxidoreductase
  4. Transfers e- from succinate to Q

    First transferred to FAD ---> FADH2 ---> 3 Fe-S clusters ---> Q

    Not enough energy to contribute to proton gradient via proton pumping

  5. Ubiquinol-cytochrome c oxidoreductase
  6. Transfers e- from QH2 to cytochrome c facing intermembrane space

    Composed of 9-10 subunits including 2 Fe-S clusters, cytochrome b560, cytochrome b566, and cytochrome c1.

    Transports 2H+ from matrix into intermembrane space

  7. Cytochrome c oxidase
  8. Contains cytochromes a and a3

    Contributes to proton gradient in two ways:

    • Pumps 2H+ for each pair of e- transferred (per O2 reduced)
    • Consumes 2H+ when oxygen is reduced to H2O ---> lowers [H+]matrix

    Carbon monoxide (CO) and cyanide (HCN) bind here

  9. ATP synthase
  10. Does not contribute to H+ gradient, but helps relieve it

    Also called FOF1 ATP synthase

    F1 component contains catalytic subunits

    FO component is proton channel that is transmembrane

    Per ATP synthesized, 3H+ move through ATP synthase

    Oligomycin - antibiotic that binds to channel and prevents proton entry --> no ATP synthesized

  • Electrons flow through ETS in direction of increasing reduction potential.
  • Two mobile electron carriers also involved: ubiquinone (Q) between complexes I or II and III, and cytochrome c between complexes III and IV.
  • Electrons enter ETS 2 at a time from either NADH or succinate.
Last modified: Wednesday, 25 January 2012, 9:42 AM