Characterization of the proteoglycans recovered under nondissociative conditions from normal articular cartilage of rabbits and dogs

Abstract

Pretreatment of articular cartilage with a highly purified collagenase in the presence of selected protease inhibitors allowed the extraction under nondissociative conditions of 65% of the tissue hexuronate. Extracted proteoglycans were purified by two successive equilibrium centrifugations in Cs2SO4 and CsCl, respectively, and then characterized by their sedimentation properties. The use of labeled proteoglycan preparations demonstrated that no detectable degradation was introduced by the new extraction procedure. When applied to growth cartilage of rachitic rats the sedimentation profile of the purified proteoglycans was practically identical to that of the proteoglycan molecules recovered by micropuncture-aspiration. Proteoglycans were extracted from normal articular cartilage of rabbits and dogs with either the new procedure or 4.0 M guanidine HCl. The purified aA1 and A1 preparations were characterized by their sedimentation properties. The aA1 contained a higher proportion of aggregates which sedimented as two distinctive populations of molecules. This bimodal distribution of the aggregates was never observed in the A1 preparations even when the dissociative extraction was performed after collagenase pretreatment of cartilages. The two extraction procedures, however, extracted the same proteoglycan monomers since the aA1-D1 and A1-D1 preparations had similar biochemical composition and g(s) distribution functions. These observations and additional in vitro aggregation studies suggested that the differences in the size and proportion of aggregates between the aA1 and A1 preparations result from a more efficient recovery of link glycoproteins in nondissociative extractions that could have determined two structurally different hyaluronate molecules.