Allows to use formate as major electron donor during aerobic respiration. Subunit gamma is probably the cytochrome b556(FDO) component of the formate dehydrogenase (By similarity). Binds 2 heme groups per subunit. Heme 1 is located at the cytoplasmic interface, heme 2 is located at the periplasmic interface. Electrons are transferred from the periplasmic to the cytoplasmic heme. Formate dehydrogenase is a membrane-bound complex, formed by subunits alpha, beta and gamma. Belongs to the formate dehydrogenase gamma subunit family.