Delineation of fucosyltransferase activities with thiol reagents

A novel method for determination of alpha1,6fucosyltransferase activity using a reducing oligosaccharide from egg yolk as a specific acceptor

A new method for determination of alpha1,6fucosyltransferase activity has been described. Recently, the disialyl-biantennary undecasaccharide was prepared in high yield from egg yolk [(1996), Carbohydr Lett 2: 137-42]. By treatment of this oligosaccharide with neuraminidase and beta-galactosidase, we readily obtained an asialo-agalacto-biantennary heptasaccharide (GlcNAcbeta 1,2Manalpha1,6[GlcNAcbeta1,2Manalpha1,3]Manbeta1 ,4GlcNAcbeta1,4GlcNAc). Using this asialo-agalacto-oligosaccharide as an acceptor, fucosyltransferases from human plasma and extracts of various human hepatoma cell lines were assayed in the presence of GDP-[3H]fucose. The reaction mixture was applied to a column of GlcNAc-binding, Psathyrella velutina lectin coupled gel. All the fucosylated acceptor were bound to the column which was eluted with 50 mM GlcNAc. Structural analyses revealed that only the innermost GlcNAc residue of the acceptor was fucosylated through an alpha1,6-linkage, and the oligosaccharide prepared could be used as a specific acceptor for alpha1,6fucosyltransferase. The present method was used to screen plasma alpha1,6fucosyltransferase in several patient groups, and significantly elevated activities were found in samples from patients with liver diseases, including chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma.

Glycosyltransferases of the human cervical epithelium. I. Characterization of a beta-galactoside alpha-2-L-fucosyltransferase and the identification of a beta-N-acetylglucosaminide alpha-3-L-fucosyltransferase

Using phenyl beta-D-galactoside as an acceptor, alpha-2-L-fucosyltransferase activity was identified in human cervical epithelium with pH optima at 6.0 and 7.2. The different response to p-chloromercuribenzoate, and ability to utilise asialofetuin as an acceptor, suggests the presence of two fucosyltransferases. The acid form is probably involved in glycoprotein synthesis in vivo. At pH 6.0, fucosyltransferase has a temperature optimum of 25 degrees C, requires the presence of Triton X-100 and either manganese or magnesium for maximal activity, and has Km values for GDP-L-[14-C]fucose and phenyl beta-D-galactoside of 32.1 . 10(-6) M and 8.2 . 10(-3) M, respectively. Guanosine nucleotides are potent inhibitors of the fucosyltransferase reaction; GDP is a competitive inhibitor while, depending on its concentration, GTP can either inhibit or activate the reaction. The alpha-L-fucosidase present in cervical tissue has negligible activity towards the enzyme product, phenyl-alpha-2-L-[14C]fucosyl-beta-D-galactoside. The use of high and low molecular weight acceptors indicates the presence of a beta-N-acetylglucosaminide alpha-3-L-fucosyltransferase and an N-acetylgalactosaminide fucosyltransferase.