SEQUENCE, TISSUE DISTRIBUTION, AND FUNCTIONAL-CHARACTERIZATION OF THERAT FRUCTOSE TRANSPORTER GLUT5

cDNA clones encoding rat GLUT5-small intestinal facilitative hexose tr ansporter were isolated from a jejunum library by cross-hybridization with a human GLUT5 cDNA probe. The cDNA sequence indicates that rat GL UT5 is composed of 502 amino acids and has 81.5% amino acid identity a nd 87.3% similarity with the sequence of human GLUT5. Expression of sy nthetic rat GLUT5 mRNA in Xenopus oocytes showed that rat GLUT5 was ab le to mediate the uptake of fructose and, to a lesser extent, of gluco se. RNA blotting studies showed that GLUT5 mRNA was present in rat sma ll intestine, kidney, and brain. Although GLUT5 mRNA is expressed in h uman testis, adipose tissue, and skeletal muscle, it could not be dete cted by RNA blotting in these rat tissues. Developmental studies showe d low levels of GLUT5 mRNA in rat small intestine and kidney during th e prenatal period with a rapid induction of GLUT5 expression occurring postnatally. In situ hybridization studies of GLUT5 mRNA expression i n the small intestine revealed differential expression along the crypt -villus axis with the highest levels of mRNA being in the midvillus re gion. In addition, there was quantitatively more GLUT5 mRNA detected i n the proximal as opposed to the distal small intestine.