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 wi th bone and teeth (osteopontin, osteocalcin and phosphophoryn) and by hydroxyapatite are examined. The proteins bound aluminum with a dissoc iation constant, K-D, of the 10(-7) M or greater at pH = 7. The number of atoms of aluminum bound was found to be related to bat not equival ent to the number of phosphorylated serines in osteopontin and phospho phoryn. Osteocalcin bound one aluminum tightly presumably due to its g amma-carboxyl glutamate residues. Hydroxyapatite bound Al3+ tightly re leasing 1.5 equivalent Ca2+ per Al3+ bound. Addition of 3 mM Ca2+, clo se to the total concentration found in animal circulating fluids, did not effect noticeably the amount of Al3+ bound to bone which mast have a K-D for Al3+ < 10(-6). Silicic acid added after equilibration With all these materials has little effect bat neither the proteins nor hyd roxyapatite removed much Al3+ from pre-equilibrated Al3+ solution with silicic acid. The results are discussed with regard to Al3+ poisoning . (C) 1997 Elsevier Science Inc.