Purification and structural characterization of a cartilage matrix protein.

The cartilage matrix protein is a major non-collagenous protein in bovine cartilage. It was purified from a 5 M-guanidinium chloride extract of bovine tracheal cartilage by sequential CsCl-density-gradient centrifugation, gel chromatography in guanidinium chloride and differential precipitation. The molecular weight of the intact protein is 148 000, determined by sedimentation-equilibrium centrifugation. It was dissociated to three subunits of molecular weight 52 000 by reduction of disulphide bonds. The cartilage matrix protein was insoluble in low-salt solutions and behaved abnormally on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The content of cysteine was high, whereas the contents of aromatic amino acids were low. The carbohydrate content was 3.9% (w/w). Glycopeptides obtained after papain digestion were heterogenous on gel chromatography. Asparagine/aspartic acid was enriched in the purified glycopeptides, indicating the presence of N-glycosidic linkages to protein.