Cytosolic phosphoglucomutase (PGM) catalyzes the reversible conversion of glucose 1-phosphate to glucose 6-phosphate. Two PGM isoenzymes, both monomers, have been identified. PGM1 is the major form found in most tissues except erythrocytes, where PGM2 is abundant (March et al. 1993; Parrington et al. 1968; Putt et al. 1993). PGM2 also has substantial phosphopentomutase activity and its primary physiological in normal tissues in vivo is not clear. Cytosolic glucose 1,6-bisphosphate synthase (PGM2L1) also possesses phosphoglucomutase activity (Maliekal et al. 2007, Veiga-da-Cunha et al. 2008).