The role of link-protein in the structure of cartilage proteoglycan aggregates

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Abstract
Proteoglycan fractions were prepared from pig laryngeal cartilage. The effect of link-protein on the properties of proteoglycan-hyaluronate aggregates was examined by viscometry and analytical ultracentrifugation. Aggregates containing link-protein were more stable than link-free aggregates at neutral pH, at temperatures up to 50.degree. C and in urea (up to 4.0 M). Oligosaccharides of hyaluronate were able to displace proteoglycans from link-free aggregates, but not from the link-stabilized aggregates. Both types of aggregate were observed in the ultracentrifuge, but at the concentration investigated (< 2 mg/ml) the link-free form was partially dissociated and the proportion aggregated varied with the pH and temperature and required more hyaluronate for saturation than did link-stabilized aggregate. Link-protein probably greatly strengthened the binding of proteoglycans to hyaluronate and under physiological conditions it locks proteoglycans on to the hyaluronate chain.