Proteinpolysaccharide Complex from Bovine Nasal Cartilage: The Function of Glycoprotein in the Formation of Aggregates

Abstract

Abstract Proteinpolysaccharide complex from bovine nasal cartilage exhibits a bimodal distribution of sedimentation coefficients when analyzed in the ultracentrifuge in associative solvents such as 0.5 m guanidinium chloride. The faster sedimenting mode disaggregates in dissociative solvents such as 4 m guanidinium chloride, giving a unimodal centrifugal pattern. Proteinpolysaccharide complex is separated into two fractions by equilibrium centrifugation in a cesium chloride gradient formed in the presence of 4 m guanidinium chloride: a glycoprotein fraction, recovered in the top of the gradient, contains 30% of the absorbance at 280 mµ of proteinpolysaccharide complex but less than 3% of the weight, while proteoglycan subunit, recovered in the bottom, contains more than 95% of the hexuronate. The subunit no longer aggregates in associative solvents, but is capable of aggregating when recombined with the glycoprotein fraction. The amount and type of aggregate formed when dissociative extracts are brought to associative conditions are determined by the pH of the extraction solvent; recovery of aggregate is maximal when extraction and reaggregation are carried out at pH 5.8. The aggregate dissociates completely when exposed to a solvent pH of 3.5 or less; disaggregation also occurs if the solvent is 2 m or greater in guanidinium chloride. The viscosities of proteinpolysaccharide complex solutions increase with increasing relative content of aggregate. Reduction and alkylation of isolated proteoglycan subunit and of the glycoprotein fraction suggest that disulfide bonds in both are required for aggregation, but that those in the former are more sensitive to reduction.