Facilitative glucose transporter, which is responsible for constitutive or basal glucose uptake. Has a very broad substrate specificity; can transport a wide range of aldoses including both pentoses and hexoses. Most important energy carrier of the brain: present at the blood-brain barrier and assures the energy-independent, facilitative transport of glucose into the brain (By similarity). In association with BSG and NXNL1, promotes retinal cone survival by increasing glucose uptake into photoreceptors (PubMed:25957687). D-glucose(out) = D-glucose(in) Interacts with isoform 1 of BSG. Retinal cones (at protein level). Belongs to the major facilitator superfamily. Sugar transporter (TC 2.A.1.1) family. Glucose transporter subfamily.