Structure and metabolism of rat liver heparan sulphate

Rat liver cells grown in primary cultures in the presence of [(35)S]sulphate synthesize a labelled heparan sulphate-like glycosaminoglycan. The characterization of the polysaccharide as heparan sulphate is based on its resistance to digestion with chondroitinase ABC or hyaluronidase and its susceptibility to HNO(2) treatment. The sulphate groups (including sulphamino and ester sulphate groups) are distributed along the polymer in the characteristic block fashion. In (3)H-labelled heparan sulphate, isolated after incubation of the cells with [(3)H]galactose, 40% of the radioactive uronic acid units are l-iduronic acid, the remainder being d-glucuronic acid. The location of heparan sulphate at the rat liver cell surface is demonstrated; part of the labelled polysaccharide can be removed from the cells by mild treatment with trypsin or heparitinase. Further, a purified plasma-membrane fraction isolated from rats previously injected with [(35)S]sulphate contains radioactively labelled heparan sulphate. A proteoglycan macromolecule composed of heparan sulphate chains attached to a protein core can be solubilized from the membrane fraction by extraction with 6m-guanidinium chloride. The proteoglycan structure is degraded by treatment with papain, Pronase or alkali. The production of heparan [(35)S]sulphate by rat liver cells incubated in the presence of [(35)S]sulphate was followed. Initially the amount of labelled polysaccharide increased with increasing incubation time. However, after 10h of incubation a steady state was reached where biosynthetic and degradative processes were in balance.