This enzyme participates in both the breakdown and synthesis of glucose. alpha-D-glucose 1-phosphate = alpha-D-glucose 6-phosphate Binds 1 Mg(2+) ion per subunit. Glucose-1,6-bisphosphate enhances phosphorylation of the active site Ser-117, and thereby increases enzyme activity. Monomer. Localizes to the junctional skeletal sarcoplasmic reticulum, probably by association with phospholipids and/or other proteins. Isoform 2 is the major calmodulin-dependent phosphoprotein in junctional skeletal sarcoplasmic reticulum vesicles. Phosphorylation at Thr-467 by PAK1 significantly enhances enzymatic activity. Belongs to the phosphohexose mutase family.