<p>This entry represents subunit C (HdrC) from CoB--CoM heterodisulphide reductase (or heterodisulphide reductase; Hdr; <db_xref db="EC" dbkey="1.8.98.1"/>), an iron-sulphur protein found in methanogenic archaea [<cite idref="PUB00044672"/>]. Hdr catalyses the reversible reduction of the heterodisulphide (CoM-S-S-CoB) to the thiol-coenzymes: coenzyme M (H-S-CoM) and coenzyme B (H-S-CoB). Hdr is composed of three subunits: hdrA (subunit A), hdrB (subunit B) and hdrC (subunit C). Hdr forms a complex with the F420-non-reducing hydrogenase (Mvh), which provides the reducing equivalents to the heterodisulphide reductase.</p><p> All processes in methanogenesis lead to the formation of a mixed disulphide bond between coenzyme-M and coenzyme-B, by a reaction in which coenzyme B reduces methyl-CoM, leading to formation of methane and a CoB-CoM heterodisulphide [<cite idref="PUB00042894"/>]. There are two different systems that are capable of reducing the CoB-CoM heterodisulphide, using either H2 or a reduced cofactor F420 as electron donors [<cite idref="PUB00044673"/>].</p><p> HdrC may carry electrons from hydrogenase to hdrA. Similar enzyme complex subunits are found in various other species, but likely act on a different substrate.</p>