May be involved in membrane fusion in exocytosis. alpha-D-glucose 1-phosphate = alpha-D-glucose 6-phosphate Binds 1 Mg(2+) ion per subunit. Phosphorylated via a calcium-dependent protein kinase. Very rapidly (within 80 ms) dephosphorylated during triggered trichocyst exocytosis. O-glycosylated with a short chain of mannose residues. Belongs to the phosphohexose mutase family.