Catalyzes the conversion of glucosamine-6-phosphate to glucosamine-1-phosphate. Also catalyzes the isomerization of glucose-1-phosphate to glucose-6-phosphate, but at a 5-fold lower rate. alpha-D-glucosamine 1-phosphate = D-glucosamine 6-phosphate Binds 1 Mg(2+) ion per subunit. Monomer. Also forms large aggregates. Activated by phosphorylation. Glucose-1,6-bisphosphate or fructose-1,6-bisphosphate can activate the enzyme in vitro. However, since glucose-1,6-bisphosphate is not believed to form in methanogens, the physiologically relevant activator might be a serine kinase protein. Belongs to the phosphohexose mutase family.