Effect of phosphorylated organic compound on the adsorption of bovine serum albumin by hydroxyapatite.

The amount of adsorption of bovine serum albumin (BSA) by hydroxyapatite (HAP) increased with a concentration of CaCl2 due to the bridging effect of Ca2+ between adsorbate BSA and adsorbent HAP. On the other hand, it decreased remarkably with a concentration of K2HPO4. This was explained in terms of the effects of ionic strength and competitive adsorption between inorganic phosphate anion (Pi) and BSA, because BSA is in negatively charged over the examined pHs. A similar effect was observed in the presence of phosphorylated compounds such as phosphoserine, phytate, and phosphorylated polyvinylalcohol. The inhibiting effect of these compounds was stronger than that of their mother compounds (serine, inositol, and polyvinylalcohol). This result shows that phosphate groups bound to the mother compounds interfere with the adsorption of BSA by HAP in the same manner that Pi does. Although the adsorption of BSA was almost irreversible with respect to dilution with water, desorption was performed when these organic phosphorylated compounds were added after the accomplishment of the adsorption of BSA. However, the effective concentration of the phosphorylated compounds for the desorption of BSA was fairly higher than that for the competitive inhibition against the BSA adsorption.