The oligosaccharides of human alpha 1-antitrypsin

Oligosaccharides were prepared from alpha 1-antitrypsin (PiM) and human serum transferrin by hydrazinolysis and then reacetylated with radiolabelled acetic anhydride. Gel permeation chromatography revealed similarities between the two preparations. The antitrypsin oligosaccharides were resolved into 76% concanavalin A binding and 24% nonbinding sugar chains by lectin affinity chromatography; both fractions were further resolved by preparative paper electrophoresis. Small amounts of neutral oligosaccharides, as well as approximately 30% "monosialo" and 67% "disialo" biantennary oligosaccharides, were identified in the lectin-binding pool. The disialo oligosaccharide fraction was susceptible to sequential degradation with exoglycosidases. Upon incubation of the monosialo biantennary oligosaccharide fraction with CMP-[14C]sialic acid and a rat liver Golgi preparation as a source of transferase, a new doubly labelled peak was formed that eluted from the gel permeation chromatography column in the same volume as the disialo biantennary oligosaccharide fraction. The paper electrophoretogram of the lectin-nonbinding oligosaccharides revealed the presence of limited amounts of neutral oligosaccharides and oligosaccharides carrying two and three negative charges. The lectin-nonbinding oligosaccharide fraction with two charges was tentatively identified as disialo biantennary oligosaccharide containing a bisecting N-acetylglucosamine residue, and the fraction with three negative charges was tentatively identified as trisialo triantennary oligosaccharide.