Intestinal epithelial cell differentiation-related changes in glycosyltransferase activities in rats

Intestinal epithelial cells differentiate as they migrate from the crypt-to-villus tip. A ten-fraction crypt-to-villus gradient of epithelial cells from rat small intestine was prepared and homogenates assayed for three glycosyltransferases involved in elongation of asparagine-linked oligosaccharides. The N-acetylglucosaminyltransferases I and II (enzymes which attach N-acetylglucosamine to either the 3' or 6' core mannose, respectively) were assayed with structurally-defined glycopeptides as specific acceptors and galactosyltransferase was assayed with asialo, agalactosylfetuin (galactose is attached to exposed N-acetylglucosamine termini). Inhibitors of glycosidases and pyrophosphatases were included in the assays to minimize effects of breakdown of substrate or product. The results indicate the N-acetylglucosaminyltransferase I shows a gradient of activity increasing from a low at the villus tip to a peak in the lower crypt region. In contrast, N-acetylglucosaminyltransferase II showed two peaks of activity, one in the villus zone and another in the upper crypt region. Galactosyltransferase activity also defined a gradient quite similar to that observed for N-acetylglucosaminyltransferase I, its specific activity being highest in the crypt cells. The specific activity levels of the three enzymes correlated with the apparent order of their action: N-acetylglucosaminyltransferase I much less than N-acetylglucosaminyltransferase II much less than galactosyltransferase. These results suggest a developmental regulation of the glycosyltransferases involved in oligosaccharide chain elongation of glycoproteins during intestinal cell differentiation.