An examination of the binding of aluminum to protein and mineral components of bone and teeth.

Aluminum binding by a variety of noncollagenous proteins associated with bone and teeth (osteopontin, osteocalcin and phosphophoryn) and by hydroxyapatite are examined. The proteins bound aluminum with a dissociation constant, KD, of the 10(-7) M or greater at pH = 7. The number of atoms of aluminum bound was found to be related to but not equivalent to the number of phosphorylated serines in osteopontin and phosphophoryn. Osteocalcin bound one aluminum tightly presumably due to its gamma-carboxyl glutamate residues. Hydroxyapatite bound Al3+ tightly releasing 1.5 equivalent Ca2+ per Al3+ bound. Addition of 3 mM Ca2+, close to the total concentration found in animal circulating fluids, did not effect noticeably the amount of Al3+ bound to bone which must have a KD for Al3+ < 10(-6). Silicic acid added after equilibration with all these materials has little effect but neither the proteins nor hydroxyapatite removed much Al3+ from pre-equilibrated Al3+ solution with silicic acid. The results are discussed with regard to Al3+ poisoning.