ADSORPTION OF LYSOZYME ONTO VARIOUS SYNTHETIC HYDROXYAPATITES

The adsorption of lysozyme (LSZ) onto various kinds of synthetic hydro xyapatite (X-10(PO4)(6)(OH)(2), denoted as CaHAP, SrHAP, and CaSrHAP f or X = Ca, Sr, and Ca + Sr, respectively) particles was investigated a t 15 degrees C in a 1 x 10(-4) mol dm(-3) KCI solution of pH 6.0. The adsorption isotherms of LSZ onto these HAPs exhibited the pseudo-langm uir type as well as those of bovine serum albumin (BSA). The negative electrophoretic mobility of the particles was reversed to a positive o ne by adsorption of positively charged LSZ molecules. No remarkable re lationship between saturated amounts of adsorbed LSZ (n(s)) and the ca tion/P molar ratio of the particles was observed on CaHAP systems, In the case of SrHAP and CaSrHAP, however, n(s) approached zero at a cati on/P molar ratio of ca. 1.70. The n(s) values of LSZ on CaHAP, SrHAP, and CaSrHAP particles are appreciably smaller than those of BSA. This study provides the first conclusive evidence that LSZ molecules specif ically adsorb onto phosphate ions on ac or be faces and/or on negative ly charged sites formed by six oxygen atoms of three phosphate ions on ab crystal faces (P sites) on the HAP surface by using basic amino gr oups, though the low probability of the latter mode was insinuated. (C ) 1997 Academic Press.