<p>This group of sequences describe a subset of formate dehydrogenase alpha chains found mainly in the archaea but also in alpha and gamma proteobacteria and a small number of Gram-positive bacteria. The alpha chain contains domains for molybdopterin dinucleotide binding and molybdopterin oxidoreductase. The holo-enzyme also contains beta and gamma subunits. 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 enzyme's purpose is to allow growth on formate in some circumstances [<cite idref="PUB00009738"/>] and, in the case of FdhH in gamma proteobacteria, to pass electrons to hydrogenase (by which process acid is neutralized) [<cite idref="PUB00009739"/>]. The alpha subunit of a version of nitrate reductase is closely related.</p>