<p>This entry consists of several bacterial and archaeal glucose-6-phosphate isomerase (GPI) proteins (<db_xref db="EC" dbkey="5.3.1.9"/>), which are involved in glycolysis and in gluconeogenesis and catalyse the conversion of D-glucose 6-phosphate to D-fructose 6-phosphate. The deduced amino acid sequence of the first archaeal PGI isolated from <taxon tax_id="2261">Pyrococcus furiosus</taxon> revealed that it is not related to its eukaryotic and many of its bacterial counterparts. In contrast, this archaeal PGI shares similarity with the cupin superfamily that consists of a variety of proteins that are generally involved in sugar metabolism in both prokaryotes and eukaryotes [<cite idref="PUB00014844"/>].</p>