The alkali-labile linkage between keratan sulphate and protein

Keratan sulphate was isolated from adult intervertebral disc in 90% yield by sequential digestion of the whole tissue with papain, Pronase and Proteus vulgaris chondroitin sulphate lyase. Treatment of this preparation with alkali cleaved a glycosidic bond between N-acetylgalactosamine and threonine and produced, by an alkali-catalysed ;peeling' reaction, an unsaturated derivative of N-acetylgalactosamine which reacted as a chromogen in the Morgan-Elson reaction, but remained covalently bonded to the keratan sulphate chain. This derivative was reduced and labelled by alkaline NaB(3)H(4). The substituent at position 3 of N-acetylgalactosamine in the keratan sulphate-protein linkage was identified as a disaccharide, N-acetylneuraminylgalactose, which was isolated from the reaction mixture after alkali treatment.