PURIFICATION AND PROPERTIES OF THE ALPHA-3 4-L-FUCOSYL-TRANSFERASE RELEASED INTO THE CULTURE-MEDIUM DURING THE GROWTH OF THE HUMAN A431 EPIDERMOID CARCINOMA CELL-LINE/

A soluble alpha-3/4-fucosyltransferase secreted into the growth medium of the human A431 epidermoid carcinoma cell line has been purified 70 0000 fold by a series of steps involving chromatography on Phenyl Seph arose 4B, CM-Sephadex C-50 and GDP-hexanolamine Sepharose 4B. The untr eated spent culture medium transferred almost ten times more fucose to the subterminal N-acetylglicosamine residue in the Type 1 (Gal beta1- 3GlcNAc) disaccharide than to the subterminal sugar in the Type 2 (Gal beta1-4GlcNAc) disaccharide; the relative activity with these two sub strates remained virtually unchanged throughout the purification proce dure. At no stage was any a-3-fucosyltransferase species acting solely on N-acetylglucosamine residues in Type 2 chains separated from the b ulk of the alpha-3/4-fucosyltransferase activity. The purified enzyme preparation showed insignificant activity with glycoprotein substrates having N-linked oligosaccharide chains with terminal Type 2 sequences but transferred fucose to a mucin-type glycoprotein with O-linked oli gosaccharide chains with terminal Type 1 structures. Lactose was a poo r substrate but the activity of the enzyme was influenced by the prese nce of substituents on the terminal beta-galactosyl residue and 2'-fuc osyllactose was almost as good an acceptor as the Type 1 disaccharide. The properties of the purified enzyme with regard to specificity, div alent cation requirements, pH optimum, and M(r), closely resembled tho se of the Lewis-blood-group gene associated a-3/4-fucosyltransferase i solated from human milk.