Heterogeneity of reducing terminals of urinary chondroitin sulfates

Human urinary chondroitin sulfates were isolated by precipitation with cetylpyridinium chloride of the non-dialyzable fraction of pooled urine, followed by ethanol fractionation and successive enzymic digestions with neuraminidase and mucopolysaccharides. Further purification was achieved by Dowex-1 chromatography with stepwise elution by increasing the concentration of NaCl at intervals of 0.25 M from 0.75 M to 1.5 M. The chondroitin sulfates thus obtained were characterized by the analysis and quantification on of carbohydrate, amino acid and sulfate, and by electrophoresis on cellulose acetate membrane. Then reducing terminals were identified by gas liquid chromatographic analyses of the acetyl and butaneboronate derivatives of hydrolysates, after reduction of the reducing terminals with sodium borohydride. About 22.8% of the urinary chondroitin sulfate in the 1.5 M fraction was peptide-bound, and the remainder was peptide-free, with xylose (29.8%), galactose (23.6%) and glucuronic acid (18.7%) at the reducing terminal. The amount of peptide-free chondroitin sulfate with xylose and galactose at its reducing terminals in the 0.75 M-, 1.0 M-, 1.25 M- and 1.5 M-fractions increased in the order described in parallel with the increase of sulfation and the decrease of peptide content. It was thus suggested that the endo-types of beta-xylosidase, beta-galactosidase and beta-glucuronidase acted on the carbohydrate-peptide linkage region of proteo-chondroitin sulfate in the tissues and produced various types of urinary chondroitin sulfate with heterogeneity at reducing terminals.