Glucosamine-6-phosphate isomerases 1 and 2 (GNPDA1, 2) catalyse the reversible deamination and with an aldo/keto isomerisation of D-glucosamine 6-phosphate (GlcN6P) to D-fructose 6-phosphate (Fru(6)P) and ammonia (NH3). GNDPA1 and 2 function as homohexamers in the cytosol. This reaction could provide a source of energy from catabolic pathways of hexosamines found in glycoproteins and glycolipids (Wolosker et al. 1998, Zhang et al. 2003, Arreola et al. 2003).