EXPRESSION OF GDP-L-FUC - GAL(BETA-1-4)GLCNAC-R (FUC TO GLCNAC) ALPHA-1,3-FUCOSYL-TRANSFERASE AND ITS RELATIONSHIP TO GLYCOPROTEIN STRUCTURE IN A HUMAN ERYTHROLEUKEMIA CELL-LINE, HEL

Terminal glycosylation may be a mechanism to control the function of s pecific biologically active glycoproteins. The biosynthesis of termina l sialyl and fucosyl residues on certain glycoproteins has been linked to the expression of the respective glycosyltransferase. In contrast, a human erythroleukemia cell line, HEL, contained a highly active GDP -L-Fuc:Gal(beta l-4)GlcNAc-R (Fuc to GlcNAc) alpha-1,3-fucosyltransfer ase (alpha-1,3-fucosyltransferase) but no detectable alpha-1,3-linked fucosyl residues on the glycoproteins. The alpha-1,3-fucosyltransferas e gave apparent K-m values for Fuc(alpha 1-2)Gal(beta 1-4)GlcNAc beta- O-benzyl, Gal(beta 1-4)GlcNAc and GDP-fucose of 0.04, 0.68 and 0.12 mM , respectively. The lack of detectable fucosyl residues in alpha-1,3-l inkage to GlcNAc on the [H-3]fucose-labeled glycoproteins was shown wi th the use of almond alpha-1,3/4-fucosidase and internal controls to v erify that the enzyme was active. Using Western-blot analysis, HEL cel l glycoproteins reacted with blood group H type-2 antibody, confirming the presence of Fuc(alpha 1-2)Gal(beta 1-4)GlcNAc as reported by othe rs and the presence of the preferred substrate for the enzyme. It is p roposed that controls for terminal glycosylation in addition to glycos yltransferase expression are operative in HEL cells and that they are part of a multi-regulated process controlling terminal modifications o f glycoproteins.