Poly(N-Acetyllactosaminyl) Oligosaccharides of Chromaffin Granule Membrane Glycoproteins

Poly(N-acetyllactosaminyl) oligosaccharides have been identified, on the basis of their susceptibility to endo-beta-galactosidase, in a large-molecular-size glycopeptide fraction derived from chromaffin granule membrane glycoproteins. The glycoproteins containing poly(N-acetyl-lactosaminyl) oligosaccharides were selectively labeled by treatment of chromaffin granule membranes with endo-beta-galactosidase to expose N-acetylglucosamine residues, followed by incubation with galactosyltransferase and UDP-[14C]galactose. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography demonstrated specific labeling in the 41-47 kilodalton (kD) region and in a distinct band at 90 kDa. Two-dimensional SDS-PAGE revealed that the poly(N-acetyllactosaminyl) oligosaccharides are predominantly present in glycoprotein IV, together with lesser labeling of glycoproteins II and III, whereas they are absent from dopamine beta-hydroxylase and carboxypeptidase H, which are the major glycoproteins of chromaffin granule membranes.