Acidic Glycoproteins from Bovine Compact Bone

Abstract

Several acidic glycoproteins with apparent molecular weights of 85,000 (bone sialoprotein, BSP), 80,000, 67,000, 60,000, 40,000 (osteonectin) and 30,000 were isolated from adult bovine compact bone. About 20-25% of the 67 K preparation was serum albumin. This contaminant was removed by passing the protein through Blue Sepharose CL-6B; the material that emerged in the void volume of this affinity column contained the bone 67 K glycoprotein free of serum albumin. All six of the proteins had high amounts of aspartic and glutamic acid. The amino acid compositions of 80 K, 67 K, 40 K and 30 K glycoproteins were very similar. The 60 K glycoprotein had an amino acid content that differed from the others with notably higher proline, alanine and valine values. All six protein samples contained mannose, galactose, glucosamine, galactosamine and sialic acid, but no fucose. The carbohydrate contents varied from about 10% for osteonectin to 38% for BSP. Antibodies were raised against electrophoretically purified osteonectin and used in enzyme-linked immunosorbent assays (ELISA). In addition to reactivity with osteonectin, the antibodies displayed strong reactivity to 80 K and 30 K glycoprotein preparations, but did not react with 67 K or 60 K bone glycoproteins or bovine serum albumin. None of the acidic glycoproteins cross-reacted with antibodies to bovine serum albumin, bovine serum proteins or human alpha 2-HS-glycoprotein.