Formate dehydrogenase allows E.coli to use formate as major electron donor during anaerobic respiration, when nitrate is used as electron acceptor. The alpha subunit FdnG contains the formate oxidation site. Electrons are transferred from formate to menaquinone in the gamma subunit (FdnI), through the 4Fe-4S clusters in the beta subunit (FdnH). Formate dehydrogenase-N is part of a system that generates proton motive force, together with the dissimilatory nitrate reductase (Nar). a quinone + formate + H(+) = a quinol + CO2 Binds 1 molybdenum-bis(molybdopterin guanine dinucleotide) (Mo-bis-MGD) cofactor per subunit. Binds 1 [4Fe-4S] cluster per subunit. Trimer of heterotrimers, consisting of subunits alpha, beta and gamma. By nitrate under anaerobic conditions. Exported by the Tat system. The position of the signal peptide cleavage has not been experimentally proven. Belongs to the prokaryotic molybdopterin-containing oxidoreductase family.