Phosphoprotein inhibition of hydroxyapatite dissolution

A chromatography column containing hydroxyapatite beads was used to study the effect of different proteins on the rate of hydroxyapatite dissolution. The four phosphoproteins tested (phosvitin, alpha sl-casein, beta-casein and kappa-casein) markedly reduced the rate of hydroxyapatite dissolution. Three nonphosphorylated proteins had a relatively smaller effect. The effect of the protein in reducing the hydroxyapatite dissolution rate has been attributed to protein binding to the surface of hydroxyapatite. The reduction in dissolution rate, expressed as the change in nmol calcium released per min per nmol of phosphoprotein bound to hydroxyapatite, increased with increasing number of phosphoserine residues of the protein. The results are consistent with the proposition that phosphoproteins have a regulatory role in mineralization processes and could provide a mechanism by which dietary and salivary phosphoproteins exert an anticariogenic effect.