Isolation and characterization of glycoproteins in proteoglycan aggregates of calf rib cartilage.

Proteoglycan aggregates were prepared under associative conditions from calf rib cartilage extracts isolated with 4 M guanidine . HCl in the presence of proteinase inhibitors. Five Coomassie blue positive bands including two link proteins could be detected after treatment of proteoglycan aggregates with 2-mercaptoethanol. After dissociating these proteoglycan aggregates with 4 M guanidine . HCl three fractions were obtained by chromatography on Sepharose 2B under the same conditions. A large complex obtained in the excluded volume was partially soluble in the presence of 0.1% sodium dodecyl sulfate, but did not enter 7.5% polyacrylamide gel. It split into seven bands; five of them were not found in proteoglycan aggregates after 2-mercaptoethanol treatment. Neither link proteins nor hyaluronate could be detected in this complex, but chondroitin sulfate was present. Proteoglycan monomers and one included fraction were isolated in addition to this complex. From the included fraction, 8 glycoproteins including 2 link proteins were isolated by preparative polyacrylamide gel electrophoresis and their amino acid and sugar contents determined. These glycoproteins possessed the ability to bind hyaluronate. These results indicate the presence of other glycoproteins besides the two link proteins and a glycoprotein-proteoglycan complex in proteoglycan aggregates of calf rib cartilage.