Catalyzes the reversible conversion of alpha-D-glucosamine 6-phosphate (GlcN-6P) into beta-D-fructose 6-phosphate (Fru-6P) and ammonium ion, a regulatory reaction step in de novo uridine diphosphate-N-acetyl-alpha-D-glucosamine (UDP-GlcNAc) biosynthesis via hexosamine pathway. Deamination is coupled to aldo-keto isomerization mediating the metabolic flux from UDP-GlcNAc toward Fru-6P. At high ammonium level can drive amination and isomerization of Fru-6P toward hexosamines and UDP-GlcNAc synthesis (PubMed:21807125, PubMed:26887390). Has a role in fine tuning the metabolic fluctuations of cytosolic UDP-GlcNAc and their effects on hyaluronan synthesis that occur during tissue remodeling (PubMed:26887390). Seems to trigger calcium oscillations in mammalian eggs. These oscillations serve as the essential trigger for egg activation and early development of the embryo (By similarity). alpha-D-glucosamine 6-phosphate + H2O = beta-D-fructose 6-phosphate + NH4(+) Allosterically activated by N-acetylglucosamine-6-phosphate (GlcNAc6P). kcat is 228 sec(-1) for conversion of alpha-D-glucosamine 6-phosphate into beta-D-fructose 6-phosphate (in the presence of GlcNAc6P). kcat is 0.14 sec(-1) for conversion of alpha-D-glucosamine 6-phosphate into beta-D-fructose 6-phosphate (in the absence of GlcNAc6P). kcat is 0.84 sec(-1) for conversion of beta-D-fructose 6-phosphate into alpha-D-glucosamine 6-phosphate (in the presence of GlcNAc6P). Nucleotide-sugar biosynthesis; UDP-N-acetyl-alpha-D-glucosamine biosynthesis; alpha-D-glucosamine 6-phosphate from D-fructose 6-phosphate: step 1/1. Homohexamer. Belongs to the glucosamine/galactosamine-6-phosphate isomerase family.