In the cytoplasm, catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate, the second step in glycolysis, and the reverse reaction during gluconeogenesis. alpha-D-glucose 6-phosphate = beta-D-fructose 6-phosphate Strongly inhibited by the polyol (sugar alcohol) phosphate D-glucitol 6-phosphate (D-sorbitol 6-phosphate) (PubMed:30240188). Also inhibited by the polyol (sugar alcohol) phosphate D-ribitol 5-phosphate (PubMed:30240188). Carbohydrate degradation; glycolysis; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-glucose: step 2/4. Homodimer. Present with 91600 molecules/cell in log phase SD medium. Belongs to the GPI family.