UDP-N-Acetyl-D-glucosamine-Asparagine sequon N-Acetyl-β-D-Glucosaminyl -Transferase-Activity in Human serum

Serum contains a sugar transferase which is able to catalyse the glycosylation in in vitro of the asparagine residue present in the sequence Asn.Leu.Thr in bovine pancreatic ribonuclease. UDP-2-Acetamido-2-deoxy-D-glucose (UDP-N-acetyl-D- glucosamine) acts as the donor, although the mechanism of the transfer is unexplored. Spermidine and Mn²⁺, as well as CDP-choline, can act as activators for the reaction. Monoglycosylated ribonuclease (ribonuclease-GIcNAc) has been separated (23% yield) from unreacted ribonuclease A by affinity chromatography on a colunm of wheat-germ agglutinin bound to Sepharose, and characterised. A possible reason for the presence of the enzyme in serum is suggested.