Proteoglycan complexes from bovine heart valve. Fractionation by density-gradient centrifugation and gel filtration under dissociative conditions.

Proteoglycan complexes from collagenase [EC 3.4.24.3]-indigestible materials of bovine heart valves were extracted with 4 M guanidinium chloride, purified by ion-exchange column chromatography in a urea-containing solution, then fractionated by density-gradient centrifugation under dissociative conditions. Electrophoretic characteristics and enzymic susceptibility of the density-gradient fractions revealed that the glycosaminoglycans constituting the proteoglycan complexes in this indigestible materials were mainly dermatan sulfate in the top three fractions, and dermatan sulfate and chondroitin sulfates in the bottom fraction; a minor constituent which was common to all the fractions was hyaluronic acid. A gel-like substance (Fr. Ig) at the top of the gradient, amounting to about 25% of the loaded dry sample, contained only a trace of hydroxyproline (less than 1%) and was composed of proteodermatan sulfate, glycoprotein, and a small amount of hyaluronic acid. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analyses of Fr. Ig with 2-mercaptoethanol showed that the major part of the proteins in this gel-like substance was cross-linked by disulfide bridges. Chromatography of Fr. Ig on Sepharose 4B in buffered 4 M guanidinium chloride containing 2-mercaptoethanol, together with the electrophoretic patterns of the resulting fractions, suggested that proteodermatan sulfate was not associated with hyaluronic acid through covalent bonds. The amino acid composition of Fr. Ig was very similar to that reported in the literature for "dermatan sulfate-protein complex", and "structural glycoprotein" or "acidic structural protein".