THE INTERACTION OF ALUMINUM WITH SILICIC-ACID IN THE PRESENCE AND ABSENCE OF A PHOSPHORYLATED PROTEIN

(1) Silicic acid alone does not bind Al3+ (10(-3) M) at pH values belo w 6.8, but above this an association is formed which is not broken by addition of the dye chrome azurol S. The precipitate which forms slowl y between silicic acid and Al3+ can be removed by centrifugation. At t his concentration (10(-3) M), Al3+ alone precipitates close to pH 7. ( 2) Phosvitin binds Al3+ at pH 5.0, with a K-D of 10(-8) M (E. Rowatt a nd R.J.P. Williams, J. Inorg. Biochem., 55 (1994) 249; T.P. Geladopoul os and T.G. Sotiroudis, J. Inorg, Biochem., 54 (1994) 247) with a rati o of Al3+ to phosvitin of 70. The complex precipitates when about half the Al3+ is added but redissolves at high concentrations of phosvitin . (3) Silicic acid does not remove Al3+ from phosvitin and phosvitin d oes not remove Al3+ from a mature precipitate of aluminosilicate, alth ough it removes some Al3+ if it is added to aluminium newly associated with silicic acid. (4) The relationships between aluminium, phosvitin and silicic acid can only be explained by taking into account the kin etics of aging of aluminium-silicic acid precipitates.