GLUT-1 MEDIATION OF RAPID GLUCOSE-TRANSPORT IN DOLPHIN (TURSIOPS-TRUNCATUS) RED-BLOOD-CELLS

D-Glucose entry into erythrocytes from adult dolphins (Tursiops trunca tus) was rapid, showed saturation at high substrate concentrations, an d demonstrated a marked stimulation by intracellular D-glucose. Kineti c parameters were estimated from the concentration dependence of initi al rates of tracer entry at 6 degrees C: for zero-trans entry, Michael is constant (K-m) was 0.78 +/- 0.10 mM and maximal velocity (V-max) wa s 300 +/- 9 mu mol.l cell water(-1).min(-1); for equilibrium exchange entry, K-m was 17.5 +/- 0.6 mM and V-max was 8,675 +/- 96 mu mol.l cel l water(-1).min(-1). Glucose entry was inhibited by cytochalasin B, an d mass law analysis of reversible, D-glucose-displaceable, cytochalasi n B binding gave values of 0.37 +/- 0.03 nmol/mg membrane protein for maximal binding and 0.48 +/- 0.10 mu M for the dissociation constant. Dolphin glucose transporter polypeptides were identified on sodium-dod ecyl sulfate-polyacrylamide gel electrophoresis immunoblots [using ant ibodies that recognized human glucose transporter isoform (GLUT-1)] as two molecular species, apparent relative molecular weights of 53,000 and 47,000. Identity of these polypeptides was confirmed by D-glucose- sensitive photolabeling of membranes with [H-3]cytochalasin B. Digesti on of both dolphin and human red blood cell membranes with glycopeptid ase F led to the generation of a sharp band of relative molecular weig ht 46,000 derived from GLUT-1, Trypsin treatment of human and dolphin erythrocyte membranes generated fragmentation patterns consistent with similar polypeptide structures for GLUT-1 in human and dolphin red bl ood cells.