Na[sup +]-Dependent Transport ofd-Xylose by Bovine Intestinal Brush Border Membrane Vesicles (BBMV) is Inhibited by Various Pentoses and Hexoses.

To detect whether pentoses and hexoses occurring in rumen bacteria or in hemicellulose ingested with feed and partly released in the small intestine have an affinity for the Na[sup +]-dependent glucose transporter of the bovine intestinal brush border membrane (BBM), we investigated whether these monosaccharides inhibit Na[sup +]-dependent transport of [sup 14]C-labelled D-xylose across the BBM using brush border membrane vesicles (BBMV) isolated from the mid-jejunum of cows. We used D-xylose as the transport substrate, because it has a low affinity for the Na[sup +]-dependent glucose transporter and thus its uptake into BBMV is more efficiently competitively inhibited by other sugars than that of D-glucose. DRibose, D-mannose and L-rhamnose occurring in rumen bacteria significantly inhibited Na[sup +]-dependent uptake of D-xylose into BBMV, but their inhibitory effect was less than that of D-glucose, D-xylose and phlorizin. This also applied to L-arabinose (and D-arabinose), which is, like D-xylose and D-galactose, a constituent of hemicellulose, and to 2-deoxy-D-glucose. Of all monosaccharides tested, only D-fructose did not affect Na[sup +]-dependent D-xylose transport. It is concluded that some pentoses and hexoses occurring in rumen bacteria (D-ribose, D-mannose and L-rhamnose) or hemicellulose (L-arabinose and D-xylose) have a low affinity for the Na[sup +]-dependent glucose transporter of the bovine BBM and may therefore be absorbed from the jejunum when released in the small intestine. [ABSTRACT FROM AUTHOR]