ENZYMATIC CHARACTERIZATION OF CMP-NEUAC-GAL-BETA-1-4GLCNAC-R ALPHA(2-3)-SIALYLTRANSFERASE FROM HUMAN PLACENTA

In this report we present the enzymatic characterization of CMP-NeuAc: Galbeta1-4GlcNAc-R alpha(2-3)-sialyl-transferase from human placenta u sing placenta membranes as an enzyme preparation. This sialyltransfera se is highly sensitive to detergents and prefers type 2 chain (Galbeta 1-4GlcNAc) over type 1 chain (Galbeta1-3GlcNAc) acceptors. Oligosaccha rides and glycopeptides were better acceptor substrates than glycoprot eins. Of the branched oligosaccharides, those with a bisected N-acetyl glucosamine (GlcNAc) structure appeared to be poorer substrates, while triantennary structures containing a Galbeta1-4GlcNAcbeta1-4Manalpha1 -3Man branch were preferred. Product characterization, using 400 MHz H -1-NMR spectroscopy, confirmed that sialic acid was introduced into th e Galbeta1-4GlcNAc-R units of the acceptor substrates in an alpha(2-3) linkage, and revealed that this sialyltransferase does not prefer eit her of the two branches of a complex type diantennary glycopeptide acc eptor for sialic acid attachment. These properties distinguish this en zyme from all other sialyltransferases characterized to date.