Abstract
The proteoglycan of articular cartilage provides this tissue with its elastic properties, and the structure of these molecules plays a major role in determining the resilience of the tissue to compression. In the present paper we have shown that the structure of the proteoglycan subunits in human articular cartilage changes considerably between the fetus and the mature adult. These changes occur gradually and are essentially complete by the end of growth. With increasing age the following changes were most pronounced: 1) a decrease in the proteoglycan content of the cartilage, 2) a decrease in the size of the proteoglycan subunit, 3) an increase in keratan sulfate relative to chondroitin sulfate, 4) an increase in 6-sulfation relative to 4-sulfation along the chondroitin sulfate chains, 5) an increase in protein relative to glycosaminoglycan, and 6) a decrease in serine and glycine and an increase in arginine content of the core protein. The susceptibility of the proteoglycan to proteolytic degradation by pepsin also showed age-related variations, but papain always produced the same degradation products. Irrespective of age, the majority of the proteoglycan subunits possessed the ability to interact with hyaluronic acid. Thus, although large structural changes take place in the glycosaminoglycan attachment region of the proteoglycan, the hyaluronic acid-binding region would appear to be relatively invariable. Decreases in the concentration, size, and charge of the proteoglycan would be expected to lower the elastic properties of the older cartilage.
Highlights
Large structural changes take place in and the high charge gives rise to strong water-binding and the glycosaminoglycan attachment region of the proteoglycan, the hyaluronic acid-binding region would appear to be relatively invariable
The tissue componentsextractedwith 4 M guanidinium chloride were subjected to CsCl density gradient centrifugation under dissociative conditions and divided into threefractions (Table 11).The fraction of highest density, Dl, is expected to contain mosotf the proteoglycan subunits, and the Extraction of Cartilage-In the fetal and newborn speci- yield of this fraction decreasedwith the age of the specimen
A similar result was with respect to size and composition. Such heterogeneity may observed for the proteoglycan of bovine cartilage
Summary
Anionic charge, whosesize is further increasedby their specific interaction with hyaluronic acid to form multimolecular aggregates (HardinghamandMuir, 1972). Underthese conditions the filtrate to give a density of 1.50 g / d , and guanidinium chloride was aggregation of bovine nasal cartilage proteoglycan with hyaluronic added so that its concentration remained a t 4 M. The redissolved in water for measurement of uronic acid content Case, degradation was performed a t a proteoglycan concentration of acetic acid a t 35°C. Specific viscosity of the proteoglycan was calculated relative to the Analytical Techniques-Uronic acid content (Table 111) was deflow time of an equal volume of buffer (Table VI). The tissue componentsextractedwith 4 M guanidinium chloride were subjected to CsCl density gradient centrifugation under dissociative conditions and divided into threefractions (Table 11).The fraction of highest density, Dl, is ex-
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