Effect of ultrafilterable fragments from chondroitinase and protease-treated aggrecan on calcium phosphate precipitation in liposomal suspensions.

Abstract

A liposome-centered endogenous precipitation method was used to investigate the effect of ultrafilterable fragments from the enzymatic digestion of rat chondrosarcoma aggrecan on the formation of insoluble calcium phosphate salts in buffered solutions at pH 7.4 and 22 degrees C. Unlike the intact aggrecan and its major chondroitin sulfate and core protein components, disaccharide units from chondroitinase degradation of the aggrecan and small (< 3 kg/mol molecular weight) fragments from protease digestion of the core structure were found to be only weakly inhibitory toward mineral formation. Corresponding reductions in Ca(2+)-binding indicate that these fragments were unable to absorb to active sites on the apatite surface for long enough periods to significantly hinder crystal growth. The data suggest that controlled enzymatic breakdown of aggrecan may be one possible mechanism by which the calcification of growth plate cartilage is allowed to advance in vivo.