Aggregation of Cartilage Proteoglycans Extracted with Lanthanum Chloride

Abstract

Large amounts of proteoglycan can be extracted from bovine nasal cartilage by stirring slices of the tissue in certain high-ionic-strength salt solutions (Sajdera & Hascall, 1969). After removal of most of the salt by dialysis, the proteoglycan can be isolated from the extract by CsCl density-gradient centrifugation (Sajdera & Hascall, 1969). This proteoglycan appears to be a macromolecular aggregate and can be dissociated in 4~-guanidine. Thus, a further CsCl centrifugation of the proteoglycan in the presence of 4 . 0 ~ guanidine allows the separation of a ‘proteoglycan subunit’ and the factors that promote its aggregation (Hascall & Sajdera, 1969). Present evidence suggests that these factors are of two types, a ‘glycoprotein link-factor’ and hyaluronic acid (Hascall & Sajdera, 1969; Hardingham & Muir, 1973; Gregory, 1973). We have previously shown that proteoglycan can be extracted from slices of bovine nasal cartilage by stirring it in 0.5w-LaC13 (Mason & Mayes, 1973). Moreover on diluting the extract to 0.05~-L,aCI,, the solubilized proteoglycan precipitates. A ‘proteoglycan subunit’ fraction can be prepared from the precipitate and its composition closely resembles that of ‘proteoglycan subunit’ fractions isolated from more conventional extracts of the tissue with 2.0M-CaC12 or 4.0w-guanidine hydrochloride (Mayes et al., 1973). Since LaClj probably solubilizes proteoglycan from cartilage by a similar mechanism to other high-ionic-strength salt solutions (see Mason & Mayes, 1973) it seemed likely that the lanthanum extract would also contain aggregation factors. We report below a simple method for isolating a fraction from 0.5 M L ~ C ~ , cartilage extracts which promotes proteoglycan aggregation. The method does not require prolonged density-gradient centrifugation and can be used for large-scale preparations.