**4.3. GLUT3** *(SLC2A3)*

GLUT3 was cloned from a human fetal muscle cDNA library. GLUT3 is considered as a neuronspecific glucose transporter due to its dominant expression in the brain in various species. However, besides the brain GLUT3 is also expressed in tissues with high demand for glucose such as testes (spermatozoa), placenta, preimplantation embryos or certain cancer cells and cancer tissues. Its tissue distribution and function correspond with its high affinity (Km=1.4 mM for 2-DG), and transport capacity for glucose. While galactose (Km=8.5 mM), mannose, maltose, xylose and dehydroascorbic acid are substrates for GLUT3, fructose is not. GLUT3 is inhibited by cytochalasin B (Ki=0.4 µM), phloretin, and and phlorizin.
