Biosynthesis of microvillus membrane-associated glycoproteins of small intestinal epithelial cells in germ-free and conventionalized mice.

We studied the effect of intestinal microorganisms on the synthesis of membrane-associated glycoproteins in the upper small intestine by intraperitoneally administering L-[3H]fucose, D-[14C]glucosamine, or L-[3H]leucine to germ-free mice and mice exposed to microorganisms for 4 weeks (conventionalized). The incorporation of the labeled compounds into sucrase-isomaltase complex and maltase was determined by immunoprecipitating Triton X-100-solubilized microvillus membranes with their antibodies. Purified microvillus membranes from germ-free and conventionalized mice differed in the activities of some marker enzymes but not in the number and mobility of the components on SDS-polyacrylamide gel electrophoresis. Maximal incorporation of [3H]fucose and [14C]glucosamine into the microvillus membrane and two enzymes was reached 2-3 h post-injection in both groups, however, the amounts incorporated were larger in conventionalized mice. There was little difference in [3H]leucine incorporation into the total glycoproteins of microvillus membranes between the two groups. Our results suggest that the introduction of microorganisms stimulates the synthesis of sugar chains of microvillus membrane-associated glycoproteins. The enhanced in vitro fucosyltransferase activity in conventionalized mice partly supports this suggestion.