<p>This enzyme family shares sequence similarity and a requirement for a molydenum cofactor as the only prosthetic group. The form of the cofactor is a single molybdenum atom coordinated by two molybdopterin guanine dinucleotide molecules. Members of the family include biotin sulphoxide reductase, dimethylsulphoxide reductase, and trimethylamine-N-oxide reductase, although a single member may show all those activities and related activities; it may not be possible to resolve the primary function for members of this family by sequence comparison alone. A number of similar molybdoproteins in which the N-terminal region contains a CXXXC motif and may bind an iron-sulphur cluster are excluded from this set, including formate dehydrogenases and nitrate reductases. Also excluded is the A chain of a heteromeric, anaerobic DMSO reductase, which also contains the CXXXC motif [<cite idref="PUB00007981"/>].</p>