<p> During dissimilatory sulphate reduction and sulphur oxidation, adenylylsulphate (APS) reductase catalyzes reversibly the two-electron reduction of APS to sulphite and AMP. Found in several bacterial lineages and in Archaeoglobales, APS reductase is a heterodimer composed of an alpha subunit containing a noncovalently bound FAD, and a beta subunit containing two [4Fe-4S] clusters. This entry describes the beta subunit of APS reductase, which shares a common evolutionary origin with other iron-sulphur cluster-binding proteins.</p>