Succinate/CoQ oxidoreductase

Complex II The second of the four membrane-bound complexes, succinate-CoQ oxidoreductase, also catalyzes the transfer of electrons to coenzyme Q. However, its source of electrons (in other words, the substance being oxidized) differs from the oxidizable substrate (NADH) acted on by NADH-GoQ oxidoreductase. In this case the substrate is succinate from the citric acid cycle, which is oxidized to fumarate by a flavin enzyme (see Figure 20.6). 

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