Effects of enzymatic digestions on the negative charge of articular cartilage surfaces.

The articular surface of adult BALB/c mouse femoral heads is covered by a fine granular electron dense material containing negative charges that bind electrostatically cationized ferritin. The material is of proteidic nature being digested by trypsin and chymopapain and resistant to testicular and microbial hyaluronidase, keratanase, chondroitinase ABC and AC. Mammalian collagenase disrupted the surface without digesting the material and allowed the penetration of cationized ferritin in the subsurface layers, where the label was bound on residual fibers. Sequential digestion with collagenase and chondroitinase ABC showed that the charges associated with the subsurface fibers are proteoglycans.