Succinate dehydrogenase

Succinate dehydrogenase is a membrane-bound enzyme complex that oxidizes succinate to fumarate and transfers the resulting electrons to ubiquinone. It functions in both the citric acid cycle and the mitochondrial respiratory chain.

Flavin adenine dinucleotide: Flavin adenine dinucleotide is a redox-active cofactor that accepts or donates electrons and hydrogen atoms. Its tightly bound flavin group accepts electrons during succinate oxidation.
Citric acid cycle: The citric acid cycle is a sequence of reactions that oxidizes acetyl groups and supplies reducing equivalents for cellular metabolism. Succinate dehydrogenase catalyzes one of the cycle’s eight central reactions.
Succinate dehydrogenase deficiency: Succinate dehydrogenase deficiency is a group of inherited disorders caused by impaired function of the enzyme complex. Defective enzyme activity can disrupt energy metabolism and cause neurological or other systemic disease.
Complex I: Complex I is a respiratory-chain enzyme that oxidizes NADH, reduces ubiquinone, and pumps protons across the inner mitochondrial membrane. Unlike Complex I, succinate dehydrogenase accepts electrons from succinate and does not pump protons.
Ubiquinone: Ubiquinone is a lipid-soluble electron carrier that moves electrons through respiratory chains in cell membranes. The enzyme passes its electrons to ubiquinone, linking its reaction to respiration.
Mitochondrial inner membrane: The mitochondrial inner membrane encloses the matrix and houses respiratory-chain complexes and transport proteins. The enzyme is embedded in this membrane, with its catalytic domain facing the matrix.
Paraganglioma: A paraganglioma is a neuroendocrine tumor arising from paraganglionic cells, often associated with inherited susceptibility genes. Inherited defects in succinate dehydrogenase subunits predispose to many paragangliomas.
Complex III: Complex III transfers electrons from ubiquinol to cytochrome c and pumps protons across the mitochondrial inner membrane. It receives ubiquinol downstream, whereas succinate dehydrogenase reduces ubiquinone.
Iron-sulfur protein: An iron-sulfur protein contains clusters of iron and sulfide that transfer electrons in biological reactions. Iron-sulfur clusters relay electrons from the flavin cofactor toward ubiquinone.
Oxidation-reduction reaction: An oxidation-reduction reaction transfers electrons between chemical species, changing their oxidation states. The enzyme couples succinate oxidation to reduction of its flavin and downstream carriers.

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