Alpha chain of the formate dehydrogenase (FDH) that catalyzes the reversible two-electron oxidation of formate to carbon dioxide. The alpha subunit of formate dehydrogenase forms the active site. 2 Fe(III)-[cytochrome c553] + formate = CO2 + 2 Fe(II)-[cytochrome c553] + H(+) Binds 1 [4Fe-4S] cluster per subunit. Binds 1 W-bis(molybdopterin guanine dinucleotide) (W-bis-MGD) cofactor per subunit. Measurements have been done with the heterotrimer complex. kcat is 262 sec(-1) with formate as substrate (at pH 7.6). Optimum pH is 9.5. Optimum temperature is 51 degrees Celsius. Heterotrimer of cytochrome c3 FDH2C and formate dehydrogenase FDH2 alpha and beta subunits that forms the FdhABC(3) complex. The trimeric FdhABC(3) complex is the main formate dehydrogenase enzyme in the presence of molybdenum. Predicted to be 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.