Human ovarian cancer, lymphoma spleen, and bovine milk GlcNAc:β1,4Gal/GalNAc transferases: Two molecular species in ovarian tumor and induction of GalNAcβ1,4Glc synthesis by α-lactalbumin

Affinity Gel-UDP was utilized to purify GlcNAc:β1,4Gal/GalNAc transferases (Ts) from human lymphoma spleen, ovarian tumor, and ovarian cancer sera. Mn²⁺ was found to be an absolute requirement for activity. Two molecular species containing both β1,4Gal/GalNAc-T activities were discernible when the purified ovarian tumor microsomal enzyme was subjected to Sephacryl S-100 HR column chromatography as well as native polyacylamide gel-electrophoresis. Acceptor specificity studies of the affinity-purified lymphoma spleen and ovarian tumor microsomal enzymes and the conventionally purified, as well as the cloned, bovine milk GlcNAc:β1,4Gal-Ts using a number of synthetic acceptors showed that the β(1,6)-linked GlcNAc moiety to α-GalNAc was the most efficient acceptor. As compared to the purified milk enzyme, the recombinant form exhibited sixfold GlcNAc:β1,4 GalNAc-T activity and up to eightfold GlcNAc6SO₃β-:β1,4Gal-T activity. Further, the recombinant enzyme catalyzed the transfer of GalNAc to the terminal β-linked GlcNAc6SO₃ moiety. Alpha-lactalbumin (α-LA) inhibited up to 85%, the transfer of Gal to the GlcNAc moiety linked either to Man or GlcNAc. On the contrary, α-LA had no significant influence on the transfer of GalNAc to the above acceptors. α-LA had no appreciable effect on the recombinant enzyme, except for the transfer of Gal or GalNAc to Glc. Both α- and β-glucosides, as well as α-N-acetylglucosaminide, did not serve as acceptors.