Involved in the first committed step in the biosynthesis of amino-sugar-nucleotides. Catalyzes the hydrolysis of the N-acetyl group of N-acetylglucosamine-6-phosphate (GlcNAc-6-P) to yield glucosamine 6-phosphate and acetate. H2O + N-acetyl-D-glucosamine 6-phosphate = acetate + D-glucosamine 6-phosphate Binds 1 divalent metal cation per subunit. Amino-sugar metabolism; N-acetylneuraminate degradation; D-fructose 6-phosphate from N-acetylneuraminate: step 4/5. Homotetramer. Belongs to the metallo-dependent hydrolases superfamily. NagA family.