The possible role of collagen fibrils and collagen-phosphoprotein complexes in the calcification of bone in vitro and in vivo.

Abstract

Samples of decalcified chicken bone containing varying concentrations of phosphoproteins from bone or egg yolk (phosvitin) were used in vitro as heterogenous nucleators for the induction induction of Ca-P apatite crystals from operationally metastable solutions of Ca and P in vitro. The lag time between exposure of the collagen-phosphoprotein complexes to a metastable solution of Ca and P and the time nucleation of crystals occurred decreased as the concentration of Ser(P) and Thr(P) increased. Enzymatic cleavage of the phosphate groups by wheat germ acid phosphatase reversed this effect, indicating that the phosphate groups per se are necessary, but may not be sufficient for the facilitation of the nucleation of Ca-P crystals by collagen complexed to phosphoprotein.