Histochemical properties of cartilage proteoglycans.

Proteoglycan interaction with alcian blue at different concentrations of magnesium chloride was studied both in vitro and in histological sections of paraffin-embedded tissues. Our experiments indicate that a) proteoglycans with different contents of chondroitin sulfate and keratan sulfate, prepared under nondegradative conditions, are not distinguishable on the basis of the critical electrolyte concentrations at which staining is abolished; b) the state of aggregation of proteoglycans only very slightly affects the alcian blue affinity of the macromolecules at different concentrations of magnesium chloride; c) the interaction of proteoglycans with other components of the connective tissue matrix is an important factor in determining the strength of binding of alcian blue to the polyanionic macromolecules in histological sections. These factors should be considered in interpreting histochemical data obtained by staining tissue sections with alcian blue at different concentrations of magnesium chloride. Proteoglycans, like glycosaminoglycans, are only weakly periodic acid-Schiff-positive.