The beta FeS subunit of formate dehydrogenase-N (FDH-N)
This subfamily contains beta FeS subunit of formate dehydrogenase-N (FDH-N), a member of the DMSO reductase family. FDH-N is involved in the major anaerobic respiratory pathway in the presence of nitrate, catalyzing the oxidation of formate to carbon dioxide at the expense of nitrate reduction to nitrite. Thus, FDH-N is a major component of nitrate respiration of Escherichia coli. This integral membrane enzyme forms a heterotrimer; the alpha-subunit (FDH-G) is the catalytic site of formate oxidation and membrane-associated, incorporating a selenocysteine (SeCys) residue and a [4Fe/4S] cluster in addition to two bis-MGD cofactors, the beta subunit (FDH-H) contains four [4Fe/4S] clusters which transfer the electrons from the alpha subunit to the gamma-subunit (FDH-I), a hydrophobic integral membrane protein, presumably a cytochrome containing two b-type heme groups.