GLUT1 Transmembrane Glucose Pathway

We synthesized a transportable diazirine derivative of D-glucose,3-deoxy-3,3-azi-D-glucopyranose (3-DAG), and studied its interaction with purified human erythrocyte facilitative glucose transporter, GLUT1. 3-DAG was rapidly transported into human erythrocytes and their resealed ghosts in the dark via a mercuric chloride-inhibitable mechanism and with a speed comparable with that of 3-O-methyl-D-glucose (3-OMG). The rate of 3-DAG transport in resealed ghosts was a saturable function of 3-DAG concentration with an apparent Km of 3.2 mM and the Vmax of 3.2 micromol/s/ml. D-Glucose inhibited the 3-DAG flux competitively with an apparent KI of 11 mM. Cytochalasin B inhibited this 3-DAG flux in a dose-dependent manner with an estimated KI of 2.4 x 10(-7) M. Cytochalasin E had no effect. These findings clearly establish that 3-DAG is a good substrate of GLUT1. UV irradiation of purified GLUT1 in liposomes in the presence of 3-DAG produced a significant covalent incorporation of 3-DAG into glut1, and 200 mM D-glucose abolished this 3-dag incorporation. Analyses of trypsin and endoproteinase Lys-C digestion of 3-DAG-photolabeled GLUT1 revealed that the cleavage products corresponding to the residues 115 183, 256 300, and 301 451 of the GLUT1 sequence were labeled by 3-DAG, demonstrating that not only the C-terminal half but also the N-terminal half of the transmembrane domain participate in the putative substrate channel formation. 3-DAG may be useful in further identification of the amino acid residues that form the substrate channel of this and other members of the facilitative glucose transporter family.