THE BETA-ANOMERIC AND GLUCOSE PREFERENCES OF GLUCOSE-TRANSPORT CARRIER FOR INTESTINAL ACTIVE ABSORPTION OF MONOSACCHARIDE CONJUGATES

The anomeric preference for intestinal absorption of glucosides and galactosides (1- and 2-naphthyl glycosides) was studied by the everted rat intestine method. After the absorption of beta-glucoside and beta- and alpha-galactosides, the glycosides itself appeared on the serosal side, whereas after the alpha-glucoside absorption, the glucoside itself was not detected on the serosal side, but a large amount of aglycone appeared instead. This indicates an alpha-anomeric preference of desglucosylation through the intestinal membrane. A significant decrease of the total (glycoside + aglycone + glucuronide metabolites) amount transported to the serosal side in the absence of Na+, a cosubstrate of the glucose transport carrier (GTC), was observed in alpha- and beta-glucosides and beta-galactoside, but not in alpha-galactoside. This indicates the poor contribution of GTC to the alpha-galactoside absorption. The Na+-dependent absorption of the glycosides by the GTC were beta-glucoside > alpha-glucoside > beta-galactoside (for 2-naphthyl glycosides), and beta-galactoside > alpha-galactoside (for 1-napthhyl glycosides). These results and those of a previous study led to the conclusion that the intestinal glucose transport carrier prefers beta-anomer to alpha-anomer, and glucose to galactose for monosaccharide conjugates absorption.