Functional and Molecular Characteristics of a Primitive Vertebrate Glucose Transporter: Studies of Glucose Transport by Erythrocytes from the Pacific Hagfish (eptatretus Stouti)

The characteristics of glucose transport were investigated in erythrocytes of a primitive vertebrate, the Pacific hagfish (Eptatretus stouti) Lockington. Transport of glucose by intact hagfish erythrocytes and by phospholipid vesicles reconstituted with noctylglucoside extract of hagfish erythrocyte membranes was rapid and mediated by a saturable stereospecific mechanism sensitive to inhibition by cytochalasin B. Covalent photoaffinity labelling experiments with [3H]cytochalasin B identified the hagfish glucose transporter on SDS/polyacrylamide gels as a protein with an apparent average Mr of 55 000. Amino acid sequence homology between the hagfish and human erythrocyte glucose transporters (GLUT 1) was investigated in immunoblotting experiments using a panel of 12 different antipeptide antisera and affinity-purified antibodies raised against cytoplasmic extramembranous regions of the human transporter, and with an antibody to the intact purified human protein. The latter antibody labelled a component in the membrane with the same apparent Mr as cytochalasin B. Two affinity-purified antipeptide antibodies, corresponding to residues 240–255 and 450–467 of the human erythrocyte transporter, also labelled a component in the membrane with this relative molecular mass, demonstrating localised sequence similarity between the polypeptides of the two species within the central cytoplasmic loop and within the cytoplasmic C-