Kandori K, Masunari A, Ishikawa T
School of Chemistry, Osaka University of Education, 4-698-1 Asahigaoka, Kashiwara, 582-8582 Osaka, Japan.
Calcif Tissue Int. 2005 Mar;76(3):194-206. doi: 10.1007/s00223-004-0102-4. Epub 2005 Feb 22.
To clarify the adsorption mechanism of proteins onto calcium hydroxyapatite (Hap), the kinetic studies of dissolution and ion-exchange properties of synthetic Hap particles in the absence and presence of proteins were examined at 15 degrees C. In the absence of proteins, Hap particles slightly dissolved to give low amounts of calcium ([Ca(2+)] = 0.09-0.14 micromol m(-2)) and phosphate [PO(4) (3-)] = 0.01-0.08 micromol m(-2)) ions in KCl, CaCl(2), BaCl(2) and AlCl(3) solutions. The [Ca(2+)] increased with increase in the Ca/P ratio of Hap, while the [PO(4) (3-)] decreased. The[ Ca(2+)] and [ PO(4) (3-)] were independent of the ionic strength. Ba(2+) and AI(3+) ions were completely ion-exchanged with calcium ions in Hap lattice within 2 hr. The solution pH was increased by 1.1-1.8 after the dissolution of OH(-) ions on the Hap surface. In the presence of bovine serum albumin (BSA), the Hap particles dissolved slightly faster than the systems without protein. This fact was explained by a complexation of dissolved ions to functional groups of BSA. The adsorption of BSA induced a reduction of [Ca(2+)] and [ PO(4) (3-)] in the aqueous medium and minima appeared on [Ca(2+)] and [PO(4) (3-)] profiles before the BSA adsorption reached a saturation. This result suggests that the adsorption of BSA onto Hap is governed by [Ca(2+)] ions complexing to BSA molecules (binding effect) together with the operation of [Ca(2+)] ions exposing on the Hap surfaces by dissolution of OH(-) ions, so-called "C-sites". The addition of BaCl(2) and AlCl(3 )steeply increased the amounts of adsorbed BSA (n(BSA)) at the initial adsorption step by the strong binding effect of these di- and tri-valent cations between BSA and Hap. However, after eliminating these cations from the Hap surface by the ion-exchange reaction, the binding effects disappeared and n(BSA) decreased. Since the number of functional groups is small, the binding effect of the counter ions was only slightly detected for the systems with di- and trivalent ions on the adsorption systems of lysozyme (LSZ).
为阐明蛋白质在羟基磷灰石（Hap）上的吸附机制，研究了15℃下合成Hap颗粒在有无蛋白质存在时的溶解及离子交换特性的动力学。在无蛋白质存在时，Hap颗粒在KCl、CaCl₂、BaCl₂和AlCl₃溶液中轻微溶解，释放出少量钙离子（[Ca²⁺]=0.09 - 0.14 μmol m⁻²）和磷酸根离子[PO₄³⁻]=0.01 - 0.08 μmol m⁻²）。[Ca²⁺]随Hap中Ca/P比的增加而增加，而[PO₄³⁻]则降低。[Ca²⁺]和[PO₄³⁻]与离子强度无关。Ba²⁺和Al³⁺离子在2小时内可与Hap晶格中的钙离子完全进行离子交换。Hap表面的OH⁻离子溶解后，溶液pH值升高1.1 - 1.8。在牛血清白蛋白（BSA）存在时，Hap颗粒的溶解速度比无蛋白质体系略快。这一现象可通过溶解离子与BSA官能团的络合作用来解释。BSA的吸附导致水相中[Ca²⁺]和[PO₄³⁻]降低，且在BSA吸附达到饱和之前，[Ca²⁺]和[PO₄³⁻]曲线出现最小值。该结果表明，BSA在Hap上的吸附受[Ca²⁺]离子与BSA分子络合（结合效应）以及Hap表面因OH⁻离子溶解而暴露的[Ca²⁺]离子（即所谓的“C位点”）的作用共同支配。在初始吸附阶段，添加BaCl₂和AlCl₃由于这些二价和三价阳离子在BSA和Hap之间的强结合作用，大幅增加了吸附的BSA量（n(BSA)）。然而，通过离子交换反应从Hap表面除去这些阳离子后，结合效应消失，n(BSA)降低。由于官能团数量较少，对于溶菌酶（LSZ）吸附体系中含有二价和三价离子的体系，仅略微检测到抗衡离子的结合效应。
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