We have isolated a clone from the rat jejunum cDNA library using a fragment of human GLUT5 cDNA as a probe. The coding region of this clone shares 80% nucleotide and 81% amino acid identity with human GLUT5 and is thus termed rat GLUT5 cDNA. Rat GLUT5 mRNA exhibited a tissue distribution very similar to that of human GLUT5, with the highest levels in the jejunum, but was not detected in fat, muscle, or testis on Northern blot analysis. The antipeptide antibody raised against the C-terminal domain of rat GLUT5 protein specifically recognized a rat jejunal protein with an apparent mol wt of 60, 000 on immunoblots. The amount of GLUT5 mRNA and protein in the jejuni of rats fed a fructose-enriched diet (50%, wt/wt) for 3 days were increased 2.5- and 6-fold, respectively, compared to those of rats fed standard rat chow, whereas those of rats fed a starch-enriched diet (50%, wt/wt) were not altered. Similarly, GLUT5 mRNA and protein in the jejunum were increased 5- and 8-fold, respectively, after 15 days of fructose feeding. Thus, an increase in fructose absorption up-regu- lates GLUT5 expression in the jejunum. These results are consistent with the notion that GLUT5 plays a major role in fructose absorption in the small intestine.
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