Goobes Rivka, Goobes Gil, Campbell Charles T, Stayton Patrick S
Department of Bioengineering, University of Washington, Seattle, Washington 98195-1721, USA.
Biochemistry. 2006 May 2;45(17):5576-86. doi: 10.1021/bi052321z.
Statherin is a salivary protein that inhibits the nucleation and growth of hydroxyapatite crystals in the supersaturated environment of the oral cavity. The thermodynamics of adsorption of statherin onto hydroxyapatite crystals have been characterized here by isothermal titration calorimetry and equilibrium adsorption isotherm analysis. At 25 degrees C, statherin adsorption is characterized by an exothermic enthalpy of approximately 3 kcal/mol that diminishes to zero at approximately 25% surface coverage. The initial heat of statherin adsorption increases with temperature, displaying a positive heat capacity change of 194 +/- 7 cal K(-)(1) mol(-)(1) at 25 degrees C. The heat of adsorption during this initial phase is strongly dependent on the buffer species, and from the differential heats of buffer ionization, it can be calculated that approximately one proton is taken up by the crystal or protein upon adsorption. The free energy of adsorption is dominated at all coverages by a large positive entropy (>or=23 cal K(-)(1) mol(-)(1)), which may be partially due to the loss of organized water that hydrates the protein and the mineral surface prior to adsorption. These results are interpreted using a two-site model for adsorption of statherin onto the hydroxyapatite crystals.
组蛋白是一种唾液蛋白，可在口腔的过饱和环境中抑制羟基磷灰石晶体的成核和生长。本文通过等温滴定量热法和平衡吸附等温线分析对组蛋白在羟基磷灰石晶体上的吸附热力学进行了表征。在25℃时，组蛋白吸附的特征是放热焓约为3千卡/摩尔，在表面覆盖率约为25%时降至零。组蛋白吸附的初始热随温度升高，在25℃时显示出194±7卡K⁻¹摩尔⁻¹的正热容变化。初始阶段的吸附热强烈依赖于缓冲液种类，根据缓冲液电离的微分热，可以计算出吸附时晶体或蛋白质大约吸收一个质子。吸附自由能在所有覆盖率下都由一个大的正熵（≥23卡K⁻¹摩尔⁻¹）主导，这可能部分是由于吸附前使蛋白质和矿物表面水合的有序水的损失。这些结果使用组蛋白在羟基磷灰石晶体上吸附的双位点模型进行解释。
