Several essential permanent cofactors in the enzyme are not shown. A portion of the flavin (FAD) is in green - it never leaves the active site, but is a permanent part of the enyzme. Succinate is oxidized to fumarate at the flavin site. A hydride (proton and its pair of electrons H-) is transferred to the flavin (with subsequent internal rearrangement in ring system). Simultaneously, a pair of electrons is drawn from a neighboring C-H bond - freeing a H+.
the results of the previous steps are shown. There is a C=C double bond in fumarate. I have show both hydrogens (one from H-, the other from H+) from succinate associated with the flavin. and now the fumarate is free to leave the active site. Electrons now start to transfer internally from cofactor to cofactor In this case I have represented the iron sulfur clusters with FeS. This is the first step electrons are quickly transferred to them and then to the heme.
The results of the previous step are shown. The flavin is back to the oxidized state and the iron sulfur clusters have been reduced (represented by FeDR). The quinone, Coenzyme Q is "dissolved" in the inner mitochondrial membrane - so this part happens at a different site than where the succinate was originally oxidized. Electrons and protons are transferred (one at a time) from the cofactors to the quinone.
The final results are shown. CoenzymeQ has been reduced to the quinol and the enzyme is back to its original state.
| Reaction | Rationale | Thermodynamics | Mechanism | Pictures | JMOL |
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Enzyme Name |
Succinate Dehydrogenase |
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Reaction Catalyzed |
Redox
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Reaction Type |
Oxidation - Reduction | |
| Pathway Involvement | Citric Acid Cycle
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| Cofactors/Cosubstrates |
Cofactors
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