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In rat small intestine, during postnatal development, the glycoprotein fucosylation is markedly increased at weaning. At the same time, a rise in the intestinal spermidine level was observed, partly due to the increase in the spermidine content of solid food given to animals at this period as compared to the spermidine content of milk. In order to mimic the spermidine increase observed in weanling rat intestines, we had treated suckling rats with spermidine by oral ingestion to study its role as maturation factor of the small intestine. In spermidine-treated suckling rats, the spermidine and N-acetyl-spermidine contents were highly increased. Spermidine treatment induced the rise in alpha-1,2-fucosyltransferase activity and the precocious appearance in the brush-border membrane of some alpha-1,2-fucoproteins in weaned rats. Such results indicate that spermidine could be a maturation factor implicated in the appearance of alpha-1,2-fucoproteins naturally observed at weaning time.

This study deals with the role of insulin in the regulation of the intestinal glycoprotein fucosylation process during postnatal development in the rat. Circulating insulin level was found to increase at weaning time in parallel with alpha-1, 2-fucosyltransferase activity and with the appearance of alpha-1, 2-fucoproteins in brush-border membranes. Insulin treatment of young suckling rats induced a precocious increase in fucosyltransferase activity and in the biosynthesis of its substrate (GDP-fucose), but the sensitivity to insulin disappeared after weaning. The insulin level was lower in 22-day-old rats that received prolonged nursing (on a high-fat diet) compared with age-matched normally weaned rats (on a high-carbohydrate diet), whereas the appearance of alpha-1, 2-fucoproteins and the increase in activity of alpha-1, 2-fucosyltransferase were delayed, as was the decrease in the degradation of GDP-fucose. In 22-day-old animals that received prolonged nursing and insulin treatment, the alpha-1, 2-fucosyltransferase activity reached a level close to that observed in age-matched weaned rats, and several alpha-1,2-fucoproteins appeared in brush-border membranes with a molecular mass similar to that found in weaned rats. These results suggest that changes in insulin levels at weaning time (as caused, in the present case, by dietary modifications) may be responsible for the regulation of the glycoprotein fucosylation process, essentially by increasing fucosyltransferase activity.

Antarctic Krill is considered as a valuable protein resource for animal and human nutrition. Due to the high content of long chain polyunsaturated fatty acids of the n-3 family, Krill consumption could be also interesting in cardiovascular diseases. In the search for the demonstration of the absence of toxicity of Krill, we studied the effect of Krill oil, as compared to fish and corn oil, on the rat intestinal fucosylation process at weaning, a very sensitive model of the influence of nutritional factors. Krill oil containing diets were very well tolerated as compared to other currently used oils and induced only slight modification in fucose and mannose proportions in intestinal glycoprotein sugars. These modifications were not reflected in the enzymatic activities involved in the fucosylation pathway. These results confirm the harmlessness of Krill derived products and their possible use in human nutrition.

High-fat diets decrease microsomic and soluble fucosyl-transferase activities in rat intestinal mucosa. This inhibition is not due to qualitative (pHi) or quantitative (relative activities) changes ion three isoenzymes, nor is it caused by alterations in the kinetic behaviour of these enzymes (Km, V). It is also not due to a direct effect of the fatty acids on the enzyme activities. It seems reasonable to suggest that a decreased biosynthesis of the fucosyl-transferase occurs as a result of the high-fat diets.

1. Rat small intestinal soluble fucosyltransferase is purified more than 2000-fold using chromatographic procedures with DEAE-cellulose, CM-cellulose, GDP-Sepharose and Concanavalin A-Sepharose. 2. Chromatography on Sephadex G15 of the final enzymatic fraction clearly separates two activities: a first peak incorporates fucose on asialoserotransferrin and a second peak on asialofetuin. 3. The use of small saccharidic acceptors (phenylgalactose, lactose, lacto-N-fucopentaose I) and the analysis of fucosylated asialoglycoproteins indicate that the first activity corresponds to an alpha-(3/4)-fucosyltransferase and the second one to an alpha-(1-2)-fucosyltransferase. 4. Protein analysis by polyacrylamide gel electrophoresis in the presence of SDS for each enzyme shows two bands corresponding to a mol. wt of about 65,000 and 70,000. The two enzymes have the same sensitivity to the action of N-ethylmaleimide.

The soluble fucosyl-transferase of the rat small intestinal mucosa was purified by passing through a Sephadex G-100 column, then resolved in two isoenzymes F1 (pHi = 4,47) and F2 (pHi = 4,96) by isoelectric focusing. The use in the first step of DEAE-cellulose instead of Sephadex G-100 leads to another component F3 (pHi = 8,70). Kinetic parameters (KM et Vm) for the three isoenzymes are given. The enzymatic mechanism seems to be a bi-bi random type for the three isoenzymes, and F3 appears as the most active species.

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 N-acetylgalactosaminyl-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 sialyl--and fucosyl-transferases with differences in specificities, varying in different ways according to age. Such developmental modifications in intestinal glycosylation patterns may be linked with certain transformation observed in the carbohydrate level of mucus or membrane-bound glycoproteins and related to the profound modifications in nutritional status at the weaning period.

To determine the effect of diets on the biosynthesis of glycoproteins in the intestinal mucosa, male Sprague-Dawley rats were fed, ad libitum, high-carbohydrate high-fat and high-protein diets. In in vivo methodology, the animals from each dietary group received an intraperitoneal injection of [14C]-fucose, or [14C]-galactose or [14C]-glucosamine. Incorporated radioactivity was detected in the different subcellular fractions. In in vitro methodology, five glycosyl-transferases were studied on microsomes and cell sap. In vivo, only the high-fat diet induces a decrease in the incorporation of [14C]-glucosamine in the macromolecules. In vitro, only the fucosyl-transferase activity is modified by several diets: as compared with an increase in the activity of the control with the age of the animals, high-protein diet induces a slight activation after 2 weeks of diet, while high-carbohydrate and particularly high-fat diets inhibit the enzyme activity. The inhibition is the same when high-fat diet consists of either oil mixture or triolein or oleic acid or linoleic acid and becomes significant with a supplementation rate of 10%.

Two groups of rats were fed either a commercial (C group) or a semi-synthetic (S group) diet of very similar quantitative composition, which induce similar growth in the animals. Glycosyltransferase activities are very different in the two groups: fucosyltransferase is lower in S group than in C group, regardless of the expression of the results (specific activity versus protein or DNA). The other activities (galactosyl-, N-acetylglucosaminyl-, N-acetylgalactosaminyltransferases) are modified when expressed versus DNA content; N-acetylneuraminyltransferase specific activity is not altered. Since the weight of mucosa is significantly lower in the S group than in the C group, all the total activities are decreased in the S group. The fucosylation process is further characterized by partial purification of the enzyme and study of the synthesis of GDP-fucose. In each case, interfering reactions (glycosyl-nucleotide pyrophosphatases and proteinases) are controlled. The results give evidence that glycosyltransferases are very sensitive to the qualitative composition of the diet.