Krebs cycle step 6

From Proteopedia

Step 6 of the Krebs cycle: Succinate Dehydrogenase

Figure: Formation of Fumarate

In the sixth step, succinate is converted to fumarate; here, a dehydrogenation takes place because two protons are removed. FAD serves as coenzyme wich is bound covalently to the enzyme succinate dehydrogenase, so that usually the notation E-FAD is used. The liberated protons (in yellow) are taken up by FAD which is oxidised to FADH₂. Unlike NADH, FADH₂ does not need to be funneled into the respiratory chain, but is reduced directly in the enzyme back to FAD, and the reaciton can take place with another succinate molecule.