Show that the free energy change for the succinate dehydroge

Show that the free energy change for the succinate dehydrogenase reaction catalyzed by Complex II is insufficient to drive ATP synthesis under standard conditions.

Solution

The reaction that produces ubiquinone from succinic acid is catalyzed by succinate dehydrogenase or complex II. The free energy change for this reaction is insufficient for ATP synthesis however this is not the case with Complex I, III and IV where free energy change is sufficient for ATP synthesis. This is due to the fact that the two electrons released when succinate is converted to fumarate are transferred first to FAD, then to Fe-S complexes, and lastly to CoQ and finally reduced CoQH₂ is formed. In this reaction, no protons are translocated across the membrane, and no proton-motive force is generated. For other complexes or enzymes, G° reaction is sufficiently negative that protons are translocated from the mitochondrial matrix across the inner membrane for each pair of electrons transferred.