Holt C, Parker T G, Dalgleish D G
Biochim Biophys Acta. 1975 Feb 27;379(2):638-44. doi: 10.1016/0005-2795(75)90170-1.
The enthalpies of reactions between alpha-s1-casein and Ca2+ in solution were measured using a gradient layer calorimeter. The reactions are exothermic between 0 and 4.3 mM CaCl2. In the region of 4.3 mM CaCl2 there is a change to an endothermic reaction corresponding to micellisation. A calcium-binding curve has been obtained under the same conditions as the calorimetry experiments and this shows two sigmoidal binding phases. Turbidity measurements show that there is an association process corresponding to the second sigmoidal phase. A tentative interpretation of the heat curve in the region before micellisation is given in terms of the site binding of Ca2+, conformational changes in the protein and association. The main thermal processes are taken to be exothermic intramolecular hydrogen bonding induced by calcium binding and endothermic hydrophobic bonding.
使用梯度层热量计测量了溶液中α-s1-酪蛋白与Ca2+之间反应的焓变。在0至4.3 mM CaCl2之间，反应是放热的。在4.3 mM CaCl2区域，反应转变为对应于胶束化的吸热反应。在与量热实验相同的条件下获得了钙结合曲线，该曲线显示出两个S形结合阶段。浊度测量表明，存在一个与第二个S形阶段相对应的缔合过程。根据Ca2+的位点结合、蛋白质的构象变化和缔合，对胶束化之前区域的热曲线进行了初步解释。主要的热过程被认为是钙结合诱导的放热分子内氢键和吸热疏水键。
