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 (By similarity). Has a role in fine tuning the metabolic fluctuations of cytosolic UDP-GlcNAc and their effects on hyaluronan synthesis that occur during tissue remodeling (By similarity). 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). Nucleotide-sugar biosynthesis; UDP-N-acetyl-alpha-D-glucosamine biosynthesis; alpha-D-glucosamine 6-phosphate from D-fructose 6-phosphate: step 1/1. Homohexamer. Widely expressed. Detected in brain, liver, kidney, muscle, ovary, testis, spermatids and spermatozoa. In spermatids, located close to the developing acrosome vesicle. In spermatozoa, found close to the acrosomal region. Belongs to the glucosamine/galactosamine-6-phosphate isomerase family.