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 (PubMed:7277315, PubMed:2344351, PubMed:8417789). Besides it's role as a glycolytic enzyme, also acts as a secreted cytokine: acts as an angiogenic factor (AMF) that stimulates endothelial cell motility (By similarity). Acts as a neurotrophic factor, neuroleukin, for spinal and sensory neurons (PubMed:3764429, PubMed:3352745). It is secreted by lectin-stimulated T-cells and induces immunoglobulin secretion (PubMed:3352745). 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 in the catalytically active form, monomer in the secreted form. ISGylated. Embryonic lethality caused by impaired gastrulation (PubMed:8922529). During early development, the egg cylinder fails to be divided into the three cavities, suggesting a deficiency in extraembryonic mesoderm formation resulting in the failure to form the amnion or chorionic mesoderm (PubMed:8922529). Belongs to the GPI family.