Chondroitin proteoglycans from squid skin. Isolation, characterization and immunological studies

Two populations of proteochondroitins were isolated from 4 M guanidine hydrochloride extracts of squid skin by a combination of ion exchange, gel chromatography and density gradient centrifugation. The proteoglycans, Mr 4.8 x 10(5) and 2.8 x 10(5), contained four and two chondroitin chains respectively and unusual oligosaccharides with uronic acid and sulphate groups, and had different amino acid and neutral sugar composition. The chondroitin chains isolated after alkaline borohydride treatment contained varying amounts of glucose, galactose, mannose, fucose and xylose, most likely as branches. Both proteoglycans were antigenic to the rabbit and showed considerable cross-reactivity as assessed by competition experiments using the ELISA technique. The proteoglycans reacted neither with exogenous hyaluronic acid nor with each other to form aggregates.