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 Carbohydrate degradation; glycolysis; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-glucose: step 2/4. Homodimer. Expressed in late sporogonial stages. Belongs to the GPI family.