There are 5 protein complexes:
- NADH-ubiquinone oxidoreductase
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
- Succinate-ubiquinone oxidoreductase
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
- Ubiquinol-cytochrome c oxidoreductase
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
- Cytochrome c oxidase
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
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.