This domain is usually found in two copies per protein. It contains up to four conserved cysteines. The group includes proteins characterised as: heterodisulphide reductase, subunit B (HrdB);succinate dehydrogenase, subunit C (SdhC, <db_xref db="EC" dbkey="1.3.99.1"/>); Fe-S oxidoreductase; glycerol-3-phosphate dehydrogenase subunit C (Anaerobic GlpC, <db_xref db="EC" dbkey="1.1.99.5"/>); and glycolate oxidase iron-sulphur subunit (GlcF) [<cite idref="PUB00007282"/>]. Cysteine-rich domain