The composition and antigenicity of sheep cortical bone matrix proteins

Sheep cortical bone powder was extracted with EDTA under mildly alkaline conditions. The extract was fractionated by CM-cellulose chromatography and caesium chloride gradient ultracentrifugation. Three chemically distinct fractions were obtained, including a sialoprotein fraction similar to that found in bovine bone. The serum proteins, albumin and immunoglobulin-G, present in trace quantities, were the most antigenic components of bone extract. Antibodies were produced in rabbits against sheep bone glycoproteins and detected by passive haemagglutination; these antibodies were weaker than those produced against articular cartilage proteins. Adsorption experiments indicated that major antigenic glycoproteins of bone matrix were not present in homologous articular cartilage tissue.