1123 bp, 8 exons

widely expressed

mitochondrial inner membrane

The complex II (succinate-ubiquinone oxidoreductase) is un key component of the mitochondrial respiratory chain and the tricarboxylic acid cycle. It is involved in the oxidation of succinate (succinate + ubiquinone = fumarate + ubiquinol) and carries electrons from FADH to CoQ. It is composed of four nuclear-encoded subunits. The subunit B protein or iron-sulfur protein, which binds three different iron-sulfur clusters, is directly involved in the catalytic activity of succinate dehydrogenase.

The complex II includes SDHD (cybS) and SDHC (cybL) which are also implicated in paragangliomas and pheochromocytomas.

Germline mutations cause hereditary paraganglioma, non-familial paraganglioma, familial and sporadic pheochromocytomas. Different germline mutations have been reported: i) a nonsense mutation (R90X) in a family with cervical paraganglioma and ectopic pheochromocytoma, ii) a missense mutation (P197R) in a family with extraadrenal pheochromocytoma and a 1bp deletion in a sporadic pheochromocytoma, iii) a missense (P131R) mutation and 1 bp insertion (M71fsX80) in familial paraganglioma and a nonsense mutation (Q59X) in sporadic paraganglioma.

Loss of wild type allele in tumor DNA is usually observed.