<p>This family of sequences describe a subset of formate dehydrogenase alpha chains found mainly in proteobacteria but also in <taxon tax_id="63363">Aquifex aeolicus</taxon>. The alpha chain contains domains for molybdopterin dinucleotide binding and molybdopterin oxidoreductase. The holo-enzyme also contains beta and gamma subunits of 32 and 20 kDa. The enzyme catalyzes the oxidation of formate (produced from pyruvate during anaerobic growth) to carbon dioxide with the concomitant release of two electrons and two protons. The electrons are utilised mainly in the nitrate respiration by nitrate reductase [<cite idref="PUB00009638"/>]. In <taxon tax_id="562">Escherichia coli</taxon> and <taxon tax_id="601">Salmonella typhi</taxon>, there are two forms of the formate dehydrogenase, one induced by nitrate which is strictly anaerobic (fdn), and one incuced during the transition from aerobic to anaerobic growth (fdo). This subunit is one of only three proteins in E. coli which contain selenocysteine [<cite idref="PUB00009639"/>].</p>