| Abstract: | 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 beta subunit of haptoglobin. 3H]Mannose-labeled haptoglobin was purified from the culture medium by immunoaffinity chromatography, and 3H]oligosaccharides were prepared by strong alkali-borohydride treatment. The oligosaccharides obtained were analyzed by anion-exchange high-performance liquid chromatography, concanavalin-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 indicate that rat haptoglobin contains two complex-type oligosaccharide chains in each beta subunit; one with a possible structure of ( +/- NeuAc----Gal beta----GlcNAc beta----)3(Man alpha----)2 Man beta----GlcNAc----( +/- Fuc alpha----)GlcNAc and the other with ( +/- NeuAc----Gal beta----GlcNAc beta----Man alpha----)2 Man beta----GlcNAc----( +/- Fuc alpha----)GlcNAc. |
