Partial characterization of matrix components interacting with cartilage proteoglycans

The charge content of aqueous suspensions of milled cartilage samples was determined by a colloid titration technique using a particle charge detector, and the data were compared with estimates from chemical analyses. Results indicated a close correlation between charge content determined by titration and that estimated by chemical analyses for samples of nasal septa only (a nonarticular cartilage). Such correlation did not hold for articular cartilages (metacarpalphalangeal joint and patella); extraction of these tissues with 0.1 or 1.2 M NaCl markedly increased the availability of the negative groups. Protein analysis, by SDS--PAGE, of the 1.2 M extracts indicated the presence of basic proteins, some of collagenous origin, such as chondrocalcin and proline-arginine-rich protein, and some of noncollagenous proteins such as pleiotrophin and histone-H2b. These data thus suggest electrostatic interactions between these basic proteins and the negative groups of proteoglycans. Such interactions would have an important effect on the osmotic properties and in the organization of cartilage.