HUMAN ERYTHROCYTES EXPRESS GLUT5 AND TRANSPORT FRUCTOSE

Although erythrocytes readily metabolize fructose, it has not been kno wn how this sugar gains entry to the red blood cell. We present eviden ce indicating that human erythrocytes express the fructose transporter GLUT5, which is the major means for transporting fructose into the ce ll. Immunoblotting and immunolocalization experiments identified the p resence of GLUT1 and GLUT5 as the main facilitative hexose transporter s expressed in human erythrocytes, with GLUT2 present in lower amounts . Functional studies allowed the identification of two transporters wi th different kinetic properties involved in the transport of fructose in human erythrocytes. The predominant transporter (GLUT5) showed an a pparent Km for fructose of approximately 10 mmol/L. Transport of low c oncentrations of fructose was not affected by 2-deoxy-D-glucose, a glu cose analog that is transported by GLUT1 and GLUT2. Similarly, cytocha lasin B, a potent inhibitor of the functional activity of GLUT1 and GL UT2, did not affect the transport of fructose in human erythrocytes. T he functional properties of the fructose transporter present in human erythrocytes are consistent with a central role for GLUT5 as the physi ological transporter of fructose in these cells. (C) 1997 by The Ameri can Society of Hematology.