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. Post-transcriptionally regulated by the GlmY/GlmZ sRNA regulatory cascade. The sRNA GlmZ, together with Hfq, directly activates glmS mRNA translation through base-pairing. A second sRNA, GlmY, positively regulates glmS indirectly, by sequestering the adapter protein RapZ and protecting GlmZ from RNA cleavage.