The isolation and characterization of the link proteins from proteoglycan aggregates of bovine nasal cartilage.

A preparation containing the link proteins may be obtained from bovine nasal cartilage by extraction with 4 M guanidine hydrochloride and by equilibrium density gradient centrifugations of the extract as commonly employed in the isolation of proteoglycan monomers. In the present paper, protein-rich proteoglycans have been removed from such a preparation to give purified link proteins by chromatography on Sepharose CL-6B in 1% sodium dodecyl sulfate. The individual link proteins, which in order of increasing electrophoretic mobility are termed link proteins 1, 2, and 3, have been separated and isolated in a subsequent preparative gel electrophoresis step. The link proteins present in largest amount, link proteins 1 and 2, have essentially the same amino acid compositions, and following partial digestion with the V8 protease from Staphylococcus aureus and analytical electrophoresis in sodium dodecyl sulfate, their peptide patterns closely resemble each other. Therefore,it is probable that link proteins 1 and 2 are structurally similar. Link protein 1 contains more carbohydrate than link protein 2 (9.5% and 3.0%, respectively) and it is suggested that the major difference between them is in carbohydrate content.