One of the major sulphated proteins secreted by rat hepatocytes contains low-sulphated chondroitin sulphate

Abstract

When isolated hepatocytes are incubated with 35SO4(2-), a specific set of secretory proteins is labelled. One of these proteins is electrophoretically heterogeneous, with an apparent molecular mass of 35-45 kDa [Marcks von Würtemberg & Fries (1989) Biochemistry 28, 4088-4093]. Here we report that treatment with chondroitinase ABC converted the broad electrophoretic band of this protein, with a 50-60% loss of radioactivity, into a relatively homogeneous band with a molecular mass of 28 kDa. Size determination by gel chromatography of the protein's oligosaccharide chain (released by alkali treatment) indicated that it contained about 40 hexose units. Similar analysis of the enzyme-resistant oligosaccharide chain remaining linked to the protein after chondroitinase ABC treatment indicated a size of between six and eight hexose units. These observations suggest that the protein's oligosaccharide chain carries only three or four sulphate groups, of which one or two are located close to the polypeptide chain. Consistent with this hypothesis, the free oligosaccharide behaved like a low-sulphated glycosaminoglycan upon ion-exchange chromatography.