Succinate-coenzyme Q reductase (EC 1.3.5.1 ; succinate dehydrogenase) is an enzyme complex found in the matrix part of the inner mitochondrial membrane. The enzyme complex has two main parts, wherein one is part of the citric acid cycle with the task of converting succinate into fumarate and the other is complex II of the electron transport chain, which uses electrons freed from succinate, to reduce ubiquinone to ubiquinol. Ubiquinol is the input of the next complex in the electron transport chain, complex III or coenzyme Q—cytochrome c reductase.

In the citric acid cycle, succinate is oxidized by the succinate dehydrogenase part of the complex and 2e^- + 2H⁺ is transferred from succinate to FAD, a coenzyme which is covalently attached to a histidine residue in the enzyme. FADH₂, the reduced form of FAD, will then transfer the two electrons to iron-sulfur clusters inside the enzyme and release the 2H⁺ back into the micochondrial matrix. The iron-sulfur clusters will reduce ubiquinone, Q, to ubiquinol, QH₂. Succinate dehydrogenase is the only membrane-bound enzyme in the TCA cycle.

External links

• Interactive Molecular model of succinate dehydrogenase (Requires MDL Chime)

Cellular respiration | Iron-sulfur proteins

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