This protein is homologous to the small subunit of NADPH and NADH forms of glutamate synthase as found in eukaryotes and some bacteria. This protein is found in numerous species having no homolog of the glutamate synthase large subunit. The prototype of the family, from Pyrococcus sp. KOD1, was shown to be active as a homotetramer and to require NADPH. [Amino acid biosynthesis, Glutamate family]