OLIGOSACCHARIDE SPECIFICITY OF NORMAL HUMAN HEPATOCYTE ALPHA-1-3 FUCOSYL-TRANSFERASE

A purified alpha1-3 fucosyltransferase (alpha1-3 FT) was recovered in the Golgi fraction of isolated hepatocytes from normal human liver tissue. The efficiency of purification was controled by measurement of fucose transfer to asialotransferrin (for alpha1-3 FT), to phenyl-beta-D-galactose (for alpha1-2 FT) and to 2' fucosyl lactose (for alpha1-3/4 FT). The initial hepatocyte isolation step got rid of 97% and 94% of alpha1-2 and alpha1-3/4 total liver FT, respectively. After Golgi enrichment (26-fold purification and a yield of 7.6%), alpha1-3 FT extract expressed a specific activity of 2 pM/min per mg protein. When incubated in optimized conditions with type 1, 2 or 6 oligosaccharide acceptors (10 mM), hepatocellular alpha-3 FT efficiently transferred fucose to N-acetyllactosamine and its 3' sialylated derivative, but poorly to lactose. When incubated with neutral or sialylated biantennary N-glycans, the enzyme expressed the highest affinity (K(m) = 0.38 mM) for the 3' bisialylated derivative. This suggests that hepatocellular alpha1-3 FT is involved in the synthesis of sialosyl Le(x) determinants on cirrhotic alpha1AGP.