PHOSPHATE ION-EXCHANGE WITH HYDROTALCITE- LIKE COMPOUND IN THE PRESENCE OF TRYPSIN

A Cl--intercalated hydrotalcite-like compound (HTAL) is a promising ma terial as a better phosphate adsorbent for further clinical use than t he currently marketed aluminum hydroxide gels. in the preceding study, we found that Cl- ions in the interlayer of HTAL can be exchanged wit h phosphate ions equivalently. In the present study, we have investiga ted the adsorption of porcine pancreas trypsin on HTAL and the influen ce of trypsin adsorption on the phosphate/Cl- ion-exchange properties of HTAL. The isotherm for trypsin adsorption at 310 K and pH 8.4 showe d the curve of BDDT V type and gave an adsorption capacity of 88.6 mg/ g for trypsin. The zeta-potential analysis of HTAL suggested that the trypsin adsorption on HTAL at pH 8.4 was restrained by the electrostat ic repulsion between HTAL surface and trypsin with positive charge. XR D and nitrogen adsorption studies showed that trypsin was adsorbed on the external surface of HTAL by occupying the area (ca. 22 nm2) per tr ypsin molecule. The phosphate/Cl- ion-exchange reaction with HTAL was not affected by the presence of trypsin; the phosphate ion-exchange ca pacity reached 73.6 mg P/g from the solution containing 3200 mg trypsi n/dm3. On the other hand, the trypsin adsorption was significantly dep ressed by the loading of phosphate ions. The XRD analysis of the phosp hate-loaded HTAL revealed that the layered structure of hydrotalcite h olds after the phosphate ion-exchange, but shows a slight increase of the interlayer distance from 0.3 nm to 0.5 nm by the intercalation of phosphate ions.