Glucose transport inhibition by proteolytic degradation of the human erythrocyte membrane inner surface

Treatment of the exterior surface of human erythrocytes with the proteolytic enzymes, trypsin or alpha-chymotrypsin (at 1 mg/ml), has no discernible effect on the carrier-mediated movement of glucose. However, the incorporation of either enzyme at much lower levels inside the erythrocyte by the method of reversible hemolysis leads to a progressive inhibition of the rate of glucose movement. Total inhibition eventually results at all tested concentrations of incorporated enzyme. These results strongly suggest that a protein susceptible to attack at the interior surface of the cell membrane is in some way involved in sugar transport. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that the spectrin band (known to be located at the inner membrane surface) gradually disappeared during the protease treatment, in close parallel with the loss in glucose transport. This was not accompanied by any appreciable modification in Band III, which has been closely identified with the glucose transport system.