Complex II of the respiratory chain, which is specifically involved in the oxidation of succinate, carries electrons from FADH to CoQ. The complex is composed of four nuclear-encoded subunits and is localized in the mitochondrial inner membrane. The subunit D protein is one of two integral membrane proteins anchoring the complex to the matrix side of the membrane. Mutations in SDHD have been linked to hereditary paraganglioma.Synonyms: CII-4, CybS, QPs3, SDH4, Succinate dehydrogenase [ubiquinone] cytochrome b small subunit mitochondrial, Succinate dehydrogenase complex subunit D, Succinate-ubiquinone oxidoreductase cytochrome b small subunit, Succinate-ubiquinone reductase membrane anchor subunit