The members of this family are similar to L-fucose isomerase expressed by E. coli (EC:126.96.36.199). This enzyme corresponds to glucose-6-phosphate isomerase in glycolysis, and converts an aldo-hexose to a ketose to prepare it for aldol cleavage. The enzyme is a hexamer, with each subunit being wedge-shaped and composed of three domains. Both domains 1 and 2 contain central parallel beta- sheets with surrounding alpha helices. The active centre is shared between pairs of subunits related along the molecular three-fold axis, with domains 2 and 3 from one subunit providing most of the substrate-contacting residues.