Catalyzes the first step in hexosamine metabolism, converting fructose-6P into glucosamine-6P using glutamine as a nitrogen source. D-fructose 6-phosphate + L-glutamine = D-glucosamine 6-phosphate + L-glutamate Homodimer. This protein undergoes a protein self splicing that involves a post-translational excision of the intervening region (intein) followed by peptide ligation. In the C-terminal section; belongs to the SIS family. GFAT subfamily.