UDP-N-acetyl-D-glucosamine-asparagine sequon N-acetyl-beta-D-glucosaminyl-transferase-activity in human serum.

Serum contains a sugar transferase which is able to catalyse the glycosylation 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 a 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-GlcNAc) has been separated (23% yield) from unreacted ribonuclease A by affinity chromatography on a column of wheat-germ agglutinin bound to Sepharose, and characterised. A possible reason for the presence of the enzyme in serum is suggested.