ences the initial attachment of microorganisms to the tooth The adsorption of lysozyme (LSZ) onto various kinds of synsurfaces and remains interposed between the enamel and thetic hydroxyapatite (X 10 (PO 4 ) 6 (OH) 2 , denoted as CaHAP, dental plaque. SrHAP, and CaSrHAP for X ร
Ca, Sr, and Ca / Sr, respectively) From this practical significance, the fundamental studies particles was investigated at 15ะC in a 1 1 10 04 mol dm 03 KCl of the adsorption of bovine serum albumin (BSA) onto varisolution of pH 6.0. The adsorption isotherms of LSZ onto these ous kinds of synthetic hydroxyapatites (HAPs), such as Ca-HAPs exhibited the pseudo-Langmuir type as well as those of HAP, strontium HAP (SrHAP), calcium-strontium HAP bovine serum albumin (BSA). The negative electrophoretic mobil-(CaSrHAP), and carbonate-containing CaHAP (CAP), ity of the particles was reversed to a positive one by adsorption of positively charged LSZ molecules. No remarkable relationship have been carried out by the authors (9-13). We clarified between saturated amounts of adsorbed LSZ ( n s ) and the cation/ in these studies that the saturated amount of adsorbed BSA, P molar ratio of the particles was observed on CaHAP systems. n s , depends on the molar ratio of cation (Ca, Sr, and/or Ca In the case of SrHAP and CaSrHAP, however, n s approached zero / Sr) to phosphorus in the materials used. The n s increased at a cation/P molar ratio of ca. 1.70. The n s values of LSZ on with increase in the cation/P molar ratio. This fact was CaHAP, SrHAP, and CaSrHAP particles are appreciably smaller explained by the electrostatic attractive forces between BSA than those of BSA. This study provides the first conclusive eviand the HAPs at pH 6. We further found that the n s depended dence that LSZ molecules specifically adsorb onto phosphate ions much more strongly on the kinds of crystal faces exposed on ac or bc faces and/or on negatively charged sites formed by at the surface of the CaHAP (13), CaSrHAP (11), and six oxygen atoms of three phosphate ions on ab crystal faces (P CAP (12) particles rather than on the cation/P values. The sites) on the HAP surface by using basic amino groups, though the low probability of the latter mode was insinuated. แญง 1997 significance of large number of positively charged adsorp-Academic Press tion sites on the exposed ac or bc crystal faces for determin-Key Words: lysozyme; adsorption; bovine serum albumin; syning the n s of BSA has been addressed in previous communithetic hydroxyapatite.
cations from our laboratory. However, the results are confined to the adsorption of BSA of an acidic protein with isoelectric point (pI) of 4.7. Since the adsorption of proteins