Structural analysis of the asparagine-linked oligosaccharides of rat haptoglobin metaholically labeled in a hepatocyte culture system.

We analyzed the asparagine-linked oligosaccharide chains of rat haptoglobin which were synthesized and secreted by hepatocytes in primary culture. When the cells were incubated with either [³H]mannose,[³H]galactose, or [³H]fucose, all the radioactive precursors were incorporated into the β subunit of haptoglobin. [³]HMannose-labled haptoglobin was purified from the culture medium by immunoaffinity chromatogrpahy, and [³H]oligosaccharides were prepared by strong alkali-borohydride treatment. The oligosccharides obtained were analyzed by anion-exchange high-performance liquid chromatography, concanavali-A - Sepharose chromatography and Bio-Gel P-4 chromatography before and after sequential exoglycosidase digestions. The oligosaccharides labeled with [³H]fucose or [³H]galactose were also characterized by the above methods. The results indicated that rat haptoglobin contains two complex-type oligosccharide chains in each β subunit one with a possible structure of (± NeuAc→Galβ→GlcNAcβ→)₃(Manα→)₂Manβ→GlcNAc→(±Fucα→)GcNAc and the other with (±NeuAc→Galβ→GlcNacβ→Manα→)₂Manβ→GlcNAc→(±Fucα→)GlcNAc. [ABSTRACT FROM AUTHOR]