Adenylylsulphate reductase, alpha subunit <p> During dissimilatory sulphate reduction or 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 alpha subunit of APS reductase, which shares a common evolutionary origin with fumarate reductase/succinate dehydrogenase flavoproteins.</p>