Activities of rat intestinal fucosyl-transferase (GDP-fucose: glycoprotein fucosyl-transferase; EC 2.4.1.68) and sialyl-transferase (N-acetylneuraminyl-transferase; EC 2.4.99.1) respectively exhibited a significant increase following weaning and a steady decrease between birth and weaning. The variations of the two glycosyl-transferase activities with age could not be explained by the presence of inhibitory factors in microsomes or cytosol, nor were they due to a natural modification of the milk composition at the end of lactation. The increase in fucosyl-transferase activity that followed weaning was prematurely induced by early weaning. Prolonged nursing prevented the normal increase in fucosyl-transferase activity, and late weaning delayed the increase. The sensitivity to the modification of the time of weaning indicated a major effect of dietary changes, related to the introduction of a solid carbohydrate-rich diet, on the developmental pattern of this enzyme. However, a stress response could not be excluded after early weaning since the corticosterone level of the early weaned rats was enhanced as compared to that of suckling rats. For sialyl-transferase, early weaning caused a slightly greater than normal decrease in the activity, whereas prolonged nursing only weakly diminished the normal decrease in the activity. Moreover, late weaning had no effect on the sialyl-transferase activity. The age-related variations of this enzyme likely are due to factors independent of diet. Thus, the developmental variations of the fucosyl- and sialyl-transferases appear to be differently regulated.

ABSTRACT. The carbohydrate composition of some intestinal glycoproteins has been demonstrated previously to be modified during development. To evaluate the role of the enzymatic mechanisms of glycosylation, the activities of three soluble and microsomal glycosyl-transferases were studied during postnatal development in rat intestinal mucosa. Nonexistent as soluble forms in the cell sap from suckling rats, the membrane-bound N-acetylgalactosaminyl-, sialyl-, and fucosyl-transferases showed different activities in microsomal fractions before weaning. The Nacetylgalactosaminyl-transferase activity was constant whereas the sialyl-transferase activity, which was maintained at a rather high level until the age of 2 wk, decreased just before weaning, while the fucosyl-transferase activity declined progressively from birth to weaning. After weaning, the three enzymatic activities progressively enhanced until adult age. Their variable behaviors on several glycoprotein acceptors may suggest the presence of several sialvl-and fucosvl-transferases with differences in soecificities, varying " I I different ways according to age. Such developmental modifications in intestinal glycosylation patterns may be linked with certain transformation ohserved in the carbohydrate level of mucus or membranebound glycoproteins and related to the profound modifications in nutritional status at the weaning period. (Pediatr Res 22: 250-256, 1987) The glycoconjugates play a prominent part in the small intestinal tract as mucus and cellular membrane components. The pre-and postnatal developmental patterns of digestive glycoprotein enzymes [such as sucrase, nialtase, isomaltase, alkaline phosphatase, or aminopeptidase (1-41 have been studied with regard to the level of enzyme activity. However, in terms of carbohydrate composition, little is known about the structure of such enzymes, except for y-glutamyl-transferase (5) and alkaline phosphatase (6, 7) which have been demonstrated to possess differences in the sialic acid content of fetal and adult-type enzymes.Modifications in the electrophoretic behavior (I) and in the glycosylation of the microvillus membrane glycoproteins (8-10) have been noted. Age-related differences in the types of mucus glycoproteins synthesized in the small intestinc were also demonstrated (I I). In all cases, the variations observed between Received September 8, 1986: accepted March 27, 1987 ' Charge dc Recherches au Centre National de la Recherche Scientifique. 2 newborn and adult animals were in glycoprotein fucosylation or sialylation. Moreover. the biosynthesis and the intracellular transport of glycoproteins were modified in rat duodenal absorptive cells as a function of age (12).Some intestinal glycosyl-transferases, responsible for the biosynthesis of carbohydrate chains of the glycoconjugates, have been well characterized ( 1 3-15). The intestinal glycosylation processes are known to depend on different factors: distribution along the intestinal tract (16) and along the crypt-to-villus axis (17, 18), admini...