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pubmed:abstractText |
beta 1,4-N-Acetylgalactosaminyltransferase (beta 1,4GalNAc-transferase) and alpha 2,3-sialyltransferase are both involved in the biosynthesis of the Sda blood group antigen, which is also present in cells of large intestine. The expression of these enzymes and of alpha 2,6-sialyltransferase activity towards N-acetyl-lactosamine was investigated in rat intestinal cells and correlated with both cell differentiation and extent of postnatal maturation. The beta 1,4GalNAc-transferase activity was exclusively found in epithelial cells of the large intestine, preferentially in the proximal segments suggesting a proximal-distal gradient of expression. The beta 1,4GalNAc-transferase and alpha 2,3-sialyltransferase activity towards N-acetyl-lactosamine were expressed in all cell fractions of the colonic crypt, with a maximum activity in the deeply located cells; therefore Sda antigen biosynthesis appears to occur preferentially at a specific stage of cell differentiation. By using N-acetyl-lactosamine as an acceptor, the predominant sialyltransferase in the colon cells was that capable of adding sialic acid in the alpha 2,3- linkage, whereas in the ileum cells the major enzyme was that forming the alpha 2,6-isomer. There were dramatic changes in the expression of colonic beta 1,4GalNac-transferase and of alpha 2,6-sialyltransferase activity towards N-acetyl-lactosamine during postnatal maturation. The former enzyme, practically absent at birth, increased slowly in the first days of life and then rapidly after weaning; by contrast, the latter enzyme was largely expressed only in newborn animals. As the colonic alpha 2,3-sialyltransferase activity towards N-acetyl-lactosamine did not change during the postnatal period, the ratio between the alpha 2,6- and alpha 2,3-sialyltransferase activities was reversed after weaning.
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