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 n-octylglucoside 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-terminal region. Glucose transport by hagfish erythrocytes was not coupled to the movement of protons.