Immobilization of galactosyltransferase and continuous galactosylation of glycoproteins in a reactor.

We immobilized human milk galactosyltransferase covalently to CNBr- and tresylchloride-activated Sepharose. The enzyme was also immobilized non-covalently to Concanavalin A-Sepharose and to monoclonal anti-galactosyltransferase antibodies which were bound via their Fc-fragment to Protein G-Sepharose. With the covalent methods, up to 72% of the enzyme could be bound to the carrier, but more than 90% of the specific activity was lost. In contrast, non-covalent immobilization yielded only about 50% immobilization efficiency, but 21% and 25% of specific activity, respectively, could be recovered. The stability of immobilized galactosyltransferase as compared to native enzyme was considerably increased: at room temperature, 55% of initial immobilized activity was lost after 65 hours compared to 95% of loss of soluble enzyme activity. Immobilized galactosyltransferase was then used for continuous galactosylation of the glycoproteins ovalbumin, endo H-treated yeast invertase and bovine serum albumin-N-acetylglucosamine in a "slurry" reactor. 55%, 35% and 25%, respectively, of all acceptor sites on these glycoproteins could be galactosylated by this method.