Proteoglycan subunits isolated by standard procedures from bovine nasal cartilage, previously incubated in the presence of [32P]phosphate contain [32]-phosphate ester groups as a regular structural component. 2. Contamination of the proteoglycan subunit with 32P-labeled nucleic acids could be excluded by repeated cesium chloride density gradient centrifugation under associative and dissociative conditions, lanthanum chloride precipitation, gel filtration and by the resistance of the proteoglycan subunit associated 32P to phosphoric diester hydrolases. 3. The [32P]phosphate ester groups are associated to the chondroitin sulfate peptide fraction obtained by proteolytic digestion of the proteoglycan subunit molecule. Degradation of the chondroitin sulfate peptide by chondroitinase ABC resulted in a 32P-labelled oligosaccharide peptide fraction, that contains xylose, galactose, glucuronic acid and inorganic phosphate in a molar ratio 1 : 2 : 1 : 0.12. 4. 32P radioactivity is released as inorganic phosphate by treatment of the 32P-labelled oligosaccharide peptide with acid phosphatase or alkali.
