A fucosyltransferase was solubilized by extraction with Triton CF-54 from a wheat-germ agglutinin-resistant variant of mouse B16 melanoma. Through affinity chromatography on GDPhexanolamine -Sepharose a 44-fold enrichment of its specific activity was obtained. Analysis of its specificity indicated that the enzyme is an N-acetylglucosaminide 3-x-~-fucosyltransferase, which is able to transfer fucose to oligosaccharides containing Gal(/l1-4)GlcNAc and Gal(j1-4)Glc structures. The enzyme is activated by divalent cations and has a maximum of activity at pH 5. It is unable to transfer fucose to sialylated glycoproteins, 6-a-sialyllactose or 3-a-sialyllactose. As suggested by its precipitation in the presence of antibodies raised in rabbit against a soluble human milk N-acetylglucosaminide 3-a-~-fucosyltransferase, these two enzymes seem to be structurally related.As recently reported [I], a wheat-germ agglutinin-resistant clone of B16 mouse melanoma demonstrated an increase in its sensitivity to the fucose-binding Lotu.r trtragonolobus lectin, as a result of a change in its glycosylation pattern involving both sialic acid and fucose. This was correlated with the observation that the variant clone demonstrated a 60 -70-fold increase in its N-acetylglucosaminide 3-x-~-fucosyltransferase activity while no other glycosyltransferase activity was modified [2].On the basis of previous studies on the specificities of glycosyltransferases, it has been suggested that the glycosylation reactions carried out by a p-galactoside 6-a-sialyltransferase, isolated from bovine milk, and an N-acetylglucosaminide 3-a-~-fucosyltransferase, isolated from human milk [3], are mutually exclusive. N o information is, however, available concerning the specificity of the corresponding 3-a-sialyltransferase. Since fucosylated structures containing the 3-a-sialyl substitution have been described [4,5], it is possible that this transferase could differ from the 6-x-sialyltransferase. Furthermore, almost 70 of the sialic acid residues present in the glycoproteins of the parent melanoma cells were demonstrated to be (~2-3)-linked to galactose [I J and the increased fucosylation of the variant cells was accompanied by a decrease of these sialyl linkages [2]. It was therefore of interest to characterize the properties of the N-acetylglucosaminide 3-a-~-fucosyltransferase and the p-galactoside 3-a-sialyltransferase of these cells in order to study the relationship of the glycosylation reactions carried out by these two enzymes. Furthermore, the highly increased activity of the fucosyltransferase in the variant cells makes
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