Mineral and collagen-binding proteins of fetal calf bone

Abstract

Subperiosteal fetal calf bone is subjected to sequential dissociative extraction in the presence of protease inhibitors first with guanidine HCl and then with guanidine HCl/EDTA. Over two-thirds of the total noncollagenous protein is recovered in the second extraction step, which operationally solubilizes proteins associated with the apatite of mineralized bone lamellae. Three new proteins, comprising over 40% of the fetal bone noncollagenous protein, are purified from the second extract by gel filtration in 4 M guanidine HCl and ion exchange in 7 M urea. These are two glycoproteins both containing organic phosphate at apparent molecular sizes of 32,000 and 62,000 daltons and a protein of 24,000 daltons containing both hydroxyproline and organic phosphate. Of these three proteins, the Mr = 32,000 species binds to apatite and collagen with the greatest affinity. It comprises 25% of the fetal calf bone noncollagenous protein and is selectively adsorbed both by apatite crystals in 4 M guanidine HCl and on gelatin affinity columns at physiological pH and ionic strength.