Immunochemical analysis of cartilage proteoglycans. Radioimmunoassay of the molecules and the substructures

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Abstract
Antibodies specifically reacting with the link proteins, the hyaluronic acid-binding region and chondroitin sulfate-peptides were used to design specific radioimmunoassay procedures. Sensitivity of the method used for the link protein was about 20 ng/ml, and the other 2 components could be determined at concentrations of about 2 ng/ml. Radioimmunoassay procedures were tested by using proteoglycan subfractions or fragments thereof. Procedures used to quantify link protein and hyaluronic acid-binding region showed no cross-interference. Fragments of trypsin-digested proteoglycan monomers still reacted in the radioimmunoassay for hyaluronic acid-binding region. Subfractions of proteoglycan monomers separated according to size had a gradually higher relative content of the hyaluronic acid-binding region, compared to both chondroitin sulphate-peptides and uronic acid, when the molecules were smaller. Proteoglycans, therefore, may contain a variably large chondroitin sulfate-rich region, which has a constant substitution with polysaccharide side chains.