Effects of Noncollagenous Proteins on Collagen Calcification.

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Effects of noncollagenous proteins of osteonectin, bone Gla protein and dentin phosphoprotein on formation of apatite were studied under three different conditions, i. e., calcifing solutions consisting of beta -glycerophosphate calcium and an alkaline phophatase enzyme, calcifing solutions consisting of inorganic calcium and phosphate, and agarose gel, in which calcium and phosphate were allowed to meet each other by diffusion. Under every condition collagen without any noncollagenous protein was found to excerpt no positive, essential effect on the formation of apatite, suggesting that collagen itself does not promote in vitro calcification. Noncollagenous proteins, when present free in solution, retarded the formation of apatite and the subsequent crystal growth as well. Apatite formed in the presence of noncollagenous proteins became smaller in crystal size, resembling that of bone and dentin in morphology. This finding may indicate that the noncollagenous proteins present free in solution play some important role in regulating crystal growth of apatite in vivo.Of the nocollagenous proteins with their movement restricted in gel, dentin phosphoprotein and phosvitin were found to promote calcification, when relatively lower concentration of calcium and phosphate was used to initiate calcification in the one-dimensional double diffusion system. The data obtained under the three different experimental conditions clearly suggest that state of noncollagenous proteins, i. e., present free in solution or present with their movement restricted, is a key point to elucidate their roles playing in in vivo calcification.