Kandori Kazuhiko, Oda Shohei, Tsuyama Shintaro
School of Chemistry, Osaka University of Education, 4-698-1 Asahigaoka, Kashiwara, 582-8582 Osaka, Japan.
J Phys Chem B. 2008 Feb 28;112(8):2542-7. doi: 10.1021/jp076421l. Epub 2008 Feb 1.
The effects of pyrophosphate ions (PP: P2O7(4-)) on the adsorption of proteins onto calcium hydroxyapatite (Hap) were examined using typical proteins of bovine serum albumin (BSA: isoelectric point (iep) = 4.7, molecular mass (M(s)) = 67 200 Da, acidic protein), myoglobin (MGB: iep = 7.0, M(s) = 17 800 Da, neutral protein), and lysozyme (LSZ: iep = 11.1, M(s) = 14,600 Da, basic protein). The UV and CD measurements determined that both the secondary and the tertiary structures of protein molecules do not vary in the presence of PP. The adsorption of BSA was strongly depressed by the addition of PP in all the methods with changing the order of PP addition. Even if BSA was pre-adsorbed on the Hap surface, PP replaced BSA molecules by strong preferential adsorption onto Hap to reduce the amounts of adsorbed BSA. A similar effect was observed with the adsorption of MGB. On the other hand, the amount of adsorbed LSZ (n(LSZ)) was increased with an increase in the concentration of PP, and the n(LSZ) value showed a maximum point in each adsorption isotherm. This fact was explained by a compression of the electric double layer (EDL) around each LSZ molecule by PP. This compression of the EDL induced the reduction of lateral electrostatic repulsions between charged LSZ molecules on the Hap surface and enhanced the formation of closed-packed monolayers to raise the n(LSZ) value. However, since the number of PPs around a LSZ molecule is decreased by an increase in the LSZ concentration in each system, the thickness of the EDL may be increased. Hence, n(LSZ) was reduced again after the maximum point in each system. Tripolyphosphate (TPP: P3O10(5-)) ions exhibited similar effects on the adsorption behaviors of all proteins, but a much more pronounced effect was observed on the LSZ system. TPP with a higher eletronegativity shielded the EDL more highly than PP to increase the n(LSZ) value. The results of the zeta potential for all the protein systems supported the modes of protein adsorption discussed.
使用牛血清白蛋白（BSA：等电点（iep）=4.7，分子量（M(s)）=67200 Da，酸性蛋白）、肌红蛋白（MGB：iep =7.0，M(s)=17800 Da，中性蛋白）和溶菌酶（LSZ：iep =11.1，M(s)=14600 Da，碱性蛋白）等典型蛋白质，研究了焦磷酸根离子（PP：P2O7(4-)）对蛋白质在羟基磷灰石（Hap）上吸附的影响。紫外和圆二色测量表明，在有PP存在的情况下，蛋白质分子的二级和三级结构均未发生变化。在所有改变PP添加顺序的方法中，添加PP都会强烈抑制BSA的吸附。即使BSA预先吸附在Hap表面，PP也会通过在Hap上的强烈优先吸附取代BSA分子，从而减少吸附的BSA量。MGB的吸附也观察到类似效果。另一方面，随着PP浓度的增加，吸附的LSZ量（n(LSZ)）增加，并且在每个吸附等温线中n(LSZ)值都出现一个最大值点。这一现象可以用PP对每个LSZ分子周围双电层（EDL）的压缩来解释。EDL的这种压缩导致Hap表面带电荷的LSZ分子之间横向静电排斥力减小，并增强了紧密堆积单层的形成，从而提高了n(LSZ)值。然而，由于每个体系中LSZ浓度的增加会减少围绕一个LSZ分子的PP数量，EDL的厚度可能会增加。因此，在每个体系中达到最大值点后，n(LSZ)又会再次降低。三聚磷酸根（TPP：P3O10(5-)）离子对所有蛋白质的吸附行为表现出类似的影响，但在LSZ体系中观察到的影响更为显著。具有更高电负性的TPP比PP更有效地屏蔽了EDL，从而增加了n(LSZ)值。所有蛋白质体系的zeta电位结果支持了所讨论的蛋白质吸附模式。
