The chemistry of connective tissues. 7. Dissociation of the chondroitin sulphate–protein complex of cartilage with alkali

Abstract

The dissocia-tion of the chondroitin sulphate-protein complex of hyaline cartilage in alkaline solution was studied by zone electrophoresis in a column stabilized by a density gradient. The complex was stable in a sodium hydroxide-sucrose solution of pH 10.8 but was irreversibly dissociated by treatment with 0.5 N-sodium hydroxide for 24 hr. at 25[degree]. It was concluded that linkage between chondroitin sulphate and protein is most probably covalent. The protein fraction released by alkaline treatment was examined by chromatography with a carboxylic acid ion-exchange resin (IRC-50). The protein was heterogeneous and appeared as a close group of poorly resolved peaks. Head and tail fractions were analyzed separately and found to have the same qualitative composition, but the head fraction contained 9.6% of carbohydrate and the tail fraction 5.4%. It was concluded that the fractions were derived from a single carbo-hydrate-containing protein which had been degraded by the action of alkali. The carbohydrate moiety of the protein was rich in glucosamine and galactose, but neutral sugars other than galactose were present in trace amount only. The core protein may thus contain keratosulphate.