Stabilization of amorphous calcium phosphate by Mg and ATP
- 353 Downloads
A synergistic effect has been demonstrated when magnesium and adenosine triphosphate (ATP) are used together in solution to delay the conversion of a slurry of amorphous calcium phosphate (ACP) to crystalline hydroxyapatite (HA). Conversion is delayed in some instances more than 10 times as long as with either ATP or Mg alone. In all experiments conversion did not begin until ATP in solution had decreased through hydrolysis to an undetectable level. The effect of Mg is to decrease substantially the rate at which ATP hydrolysis occurs. Once conversion began it proceeded more slowly in the presence of both Mg and ATP than with Mg or ATP alone. ATP was also found to prevent the formation of HA from metastable solutions of calcium and phosphate which did not contain any solid phase. Over the time period of these experiments, ATP hydrolyzed to a negligible extent in Tris-HCl buffer and in solutions containing Ca, PO4, and Ca plus PO4 ions. Hydrolysis of ATP does occur in the presence of ACP or HA, presumably by transphosphorylation on the surface of the solid calcium phosphate phase. It was concluded that ATP stabilized ACP, not by affecting its dissolution, but either by poisoning heteronuclear growth sites, or by poisoning the growth of embryonic HA nuclei (formed heterogeneously or homogeneously) before their critical size is reached, or by poisoning both. In the case of embryonic HA nuclei, the poisoned nuclei would go back into solution preventing HA crystal formation. In addition, it was found that the neutral Ca9(PO4)6 clusters, which are believed to be the basic structural unit of ACP, break down into individual Ca and PO4 ions when ACP dissolves in aqueous medium.
Key wordsStabilization Amorphous calcium phosphate Mitochondria Mg and ATP Nucleation poisoning
Unable to display preview. Download preview PDF.
- 2.Bergmeyer, H.U.: Methods of enzymatic analysis, p. 541. New York: Academic Press 1965Google Scholar
- 3.Betts, F., Blumenthal, N.C., Posner, A.S., Becker, G.L., Lehninger, A.L.: Atomic structure of intracellular amorphous calcium phosphate deposits. Proc. nat. Acad. Sci. (Wash.)72, 2088–2090 (1975)Google Scholar
- 4.Betts, F., Posner, A.S.: A structural model for ACP. Trans. Amer. Cryst. Assoc.10, 73–84 (1974)Google Scholar
- 10.Eanes, E.D., Gillessen, I.H., Posner, A.S.: Intermediate stages in the precipitation of hydroxyapatite. Nature (Lond.)208, 365–367 (1965)Google Scholar
- 11.Eanes, E.D., Posner, A.S.: Kinetics and mechanism of concersion of non-crystalline calcium phosphate to crystalline hydroxyapatite. Trans N.Y. Acad. Sci.28, 233–241 (1965)Google Scholar
- 12.Francis, M.D., Briner, W.S., Gray, J.A.: Chemical agents in the control of calcification processes in biological systems. In: Hard tissue growth, repair and remineralization, pp. 57–90. Amsterdam: Elsevier 1973Google Scholar
- 14.Lehninger, A.L.: The mitochondrion, p. 163. New York: W.A. Benjamin 1964Google Scholar
- 18.Walaas, E.: Stability constants of metal complexes with mononucleotides. Acta chem. scand.12, 528–536 (1958)Google Scholar