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Succinate dehydrogenase or succinate-coenzyme Q reductase or respiratory Complex II is an enzyme complex, found in many bacterial cells and in the inner mitochondrial membrane of eukaryotes. It is the only enzyme that participates in both the citric acid cycle and the electron transport chain.

succinate dehydrogenase (succinate-ubiquinone oxidoreductase)
Succinate Dehydrogenase 1YQ3 and Membrane.png
The structure of SQR in a phospholipid membrane. SdhA, SdhB, SdhC and SdhD
Identifiers
EC number 1.3.5.1
CAS number 9028-11-9
Databases
IntEnz IntEnz view
BRENDA BRENDA entry
ExPASy NiceZyme view
KEGG KEGG entry
MetaCyc metabolic pathway
PRIAM profile
PDB structures
Gene Ontology

Succinate dehydrogenase or succinate-coenzyme Q reductase (SQR) or respiratory Complex II is an enzyme complex, found in many bacterial cells and in the inner mitochondrial membrane of eukaryotes. It is the only enzyme that participates in both the citric acid cycle and the electron transport chain.

In step 6 of the citric acid cycle, SQR catalyzes the oxidation of succinate to fumarate with the reduction of ubiquinone to ubiquinol. This occurs in the inner mitochondrial membrane by coupling the two reactions together.