Effects of Ionic Flow and Amelogenins on the Lengthwise Growth of Octacalcium Phosphate Crystals in a Model System of Tooth Enamel Formation

摘要

This paper briefly reviews our recent studies, which aimed to investigate the effects of 1) the Ca~(2+) and PO_4~(3-) ions flow and 2) amelogenins on the lengthwise growth of octacalcium phosphate (OCP), which is a potent precursor of enamel apatite crystal. OCP crystals were grown at 37℃ in a dual membrane system under various amount of ionic inflow into a reaction space, using 1) 5-30mM Ca and PO_4 solutions as ionic sources and 2) extracted bovine amelogenin and recombinant murine amelogenins (rM179, rM166). With an increase in the amount of Ca~(2+) and/or PO_4~(3-) ions flow, the length of OCP crystal increased, while the width decreased. As a result, the length to width (L/W) ratio of crystal changed from 3 to 95, while the width to thickness (W/T) ratio from 32 to 9. The effect of amelogenins was unique, regardless of the type of amelogenins : Rod-like and prism-like OCP crystals with large L/W (61～107) and small W/T (1.3～2.2) ratios were formed in 10% amelogenin gels. In contrast, characteristic ribbon-like OCP crystals grew without protein and with gelatin, albumin, polyacrylamide gel and agarosc gel. Specific interaction of amelogenins with OCP crystal was ascribed to the self-assembly property of amelogenin molecules and their hydrophobic nature. It was suggested that ionic flow and amelogenins play some critical roles in the elongated growth of enamel crystals.