A flavoprotein (FAD) complex containing iron-sulfur centres. The enzyme is found in the inner mitochondrial membrane in eukaryotes and the plasma membrane of many aerobic or facultative bacteria and archaea. It catalyses succinate oxidation in the citric acid cycle and transfers the electrons to quinones in the membrane, thus constituting a part of the aerobic respiratory chain (known as complex II). In vivo the enzyme uses the quinone found in the organism - eukaryotic enzymes utilize ubiquinone, bacterial enzymes utilize ubiquinone or menaquinone, and archaebacterial enzymes from the Sulfolobus genus use caldariellaquinone. cf. EC
1.3.5.4, fumarate reductase (quinol).
