NapF, iron-sulfur subunit of periplasmic nitrate reductase
This family contains NapF protein, the iron-sulfur subunit of periplasmic nitrate reductase. The periplasmic nitrate reductase NapABC of Escherichia coli likely functions during anaerobic growth in low-nitrate environments; napF operon expression is activated by cyclic AMP receptor protein (Crp). NapF is a subfamily of the beta subunit of DMSO reductase (DMSOR) family. DMSOR family members have a large, periplasmic molybdenum-containing alpha subunit as well as a small beta FeS subunit, and may also have a small gamma subunit. The beta subunit contains four Fe4/S4 and/or Fe3/S4 clusters which transfer the electrons from the alpha subunit to a hydrophobic integral membrane protein, presumably a cytochrome containing two b-type heme groups. The reducing equivalents are then transferred to menaquinone, which finally reduces the electron-accepting enzyme system.