A novel assay for the biosynthesis of sulphated polysaccharide and its application to studies on the effects of somatomedin on cultured cells.

1. A simple method is described for the determination of small amounts of [(35)S]sulphated polysaccharide with 95-100% recovery in the range from 0.3 to 150mug of polysaccharide. 2. The method is based on precipitation with cetylpyridinium chloride of polysaccharide samples applied to filter paper. It is not significantly disturbed by the presence in the sample of a large excess of inorganic (35)SO(4) (2-). 3. Sulphated glucosamino- and galactosaminoglycans may be determined separately by treatment of the sample with chondroitinase ABC. 4. The method is applicable to the assay of [(35)S]sulphated polysaccharide biosynthesis in cell cultures. A stimulation of sulphate incorporation obeying a linear dose-response curve, was demonstrated in somatomedin-incubated fibroblast and glia cell cultures. 5. The described system provides a new assay method for somatomedin. 6. The stimulatory effect of somatomedin on the synthesis of [(35)S]sulphated polysaccharide appeared to be general, rather than specific, for a particular type of polysaccharide.