The isolation of "link proteins" from bovine nasal cartilage

Methods of isolating the water insoluble 'link proteins' from preparations of bovine nasal cartilage proteoglycan aggregates have been investigated. Upon chromatography on Sepharose 4B in 0.1% sodium dodecyl sulfate, the 'link proteins' are found in a discrete, included peak, whereas the bulk of the proteoglycan emerges at the void volume. Some low molecular weight proteoglycan is associated with the 'link proteins'. An alternative procedure, i.e. chromatography on DEAE-cellulose in sodium dodecyl sulfate, has also been examined. In 0.1% sodium dodecyl sulfate, proteoglycan monomer is not absorbed by the column, whereas 'link proteins' are. Subsequently, the 'link proteins' with a minor fraction of the proteoglycan are eluted with 1.0% sodium dodecyl sulfate. Both procedures serve to separate the 'link proteins' from the bulk of proteoglycan present in an aggregate preparation, but additional steps are necessary to achieve homogeneity. Thus a 'link protein' preparation, fractionated from proteoglycan aggregate by equilibrium density gradient centrifugation under dissociative conditions, can be finally purified by chromatography on DEAE-cellulose in sodium dodecyl sulfate.