Intestinal transport of beta-thioglycosides by Na+/glucose cotransporter

Intestinal metabolism and transport of p-nitrophenyl beta-D-thioglucoside ( p-NP beta Sglc) and p-nitrophenyl beta-D-thiogalactoside (p-NP beta Sgal) b y the Na+/glucose cotransporter were studied in excised small intestine of the rat. p-NP beta Sglc and p-NP beta Sgal were stable enough on the mucosal side to be transported to the serosal side. Transport of p-NP beta Sglc was inhibi ted in the presence of phloridzin (a Na+/glucose cotransporter inhibitor), glucose, or 3-O-methylglucose (3-OMG). p-NP beta Sglc transport was depende nt on Na concentration in a sigmoidal manner. The activation energy for tra nsport was 19.4 kcal mol(-1). The distribution of transport activity of p-N P beta Sglc in each region of the small intestine correlated well with that of 3-OMG. These results indicate that p-NP beta Sglc is transported by the Na+/glucose cotransporter in small intestine. The order of turnover rate f or glycoside transport by Na+/glucose cotransporter was 3-OMG > p-nitrophen yl beta-O-glucoside > p-NP beta Sglc > p-NP beta Sgal, indicating that the presence of a galactose moiety and a sulphur between the monosaccharide moi ety and aglycone decreases the turnover rate of the Na+/glucose cotransport er in the transport of glycosides. In an inhibition study using stable p-NP beta Sglc as a Na+/glucose cotransporter-transportable marker glucoside, i t was also shown that the Na+/glucose cotransporter recognized several type s of glycosides. In conclusion, displacement of the oxygen at carbon C-1 of glucose by sulph ur in thioglycosides decreases the turnover rate of the Na+/glucose cotrans porter, but thioglycosides are stable in the small intestine and are transp orted by the Na+/glucose cotransporter.