Influence of phytate on the adsorption of human salivary mucins onto hydroxyapatite.

The effect of phytate on the adsorption of purified human salivary mucins (HWSM) onto hydroxyapatite (HAP) was studied using three incubation conditions. a. Preadsorption of HWSM onto HAP for 24 h, followed by 4 h coadsorption with phytate, resulted in at most a 25% decrease in HWSM binding. b. Preincubation of HAP with phytate for 24 h, followed by 4 h coadsorption with HWSM, resulted in a 40% decrease in binding of HWSM to HAP. c. Simultaneous incubation of HWSM and phytate with HAP resulted in a 50% decrease in HWSM binding. In contrast, the adsorption of phytate to HAP was not affected, irrespective of the incubation set up used. The adsorption of phytate to hydroxyapatite was accompanied by an increase in the phosphate concentration of the solution. The molar ratio of phosphate solubilized/phytate bound to HAP was approximately 2 to 3. On the other hand, under conditions when all phytate added became bound to HAP (i.e. HAP in excess over phytate), no increase in Ca-ions was observed. However, when free phytate was present (phytate in excess over HAP) approximately one mole of Ca-ions was released per mole free phytate. For comparison, the effect of phytate on the adsorption of porcine gastric mucin (PGM) and ovine submandibular mucin (OSM) was studied. Under conditions when HWSM binding to HAP was decreased by 10%, binding of PGM and OSM decreased by 65% and 100%, respectively.