Department of Food Science and Technology, University of Tennessee, Knoxville, Tennessee 37996, United States.
J Agric Food Chem. 2013 Jan 30;61(4):947-54. doi: 10.1021/jf303844w. Epub 2013 Jan 16.
Binding between β-lactoglobulin (β-Lg), the major whey protein, and bixin, the major carotenoid in annatto, was studied at pH 3.0-10.0. The Fourier transform infrared spectroscopy and UV-vis absorption spectroscopy results showed that the binding involved a complex formation. The tryptophan quenching fluorescence and analytical ultracentrifugation data showed that there were two specific binding sites and that the binding affinity increased significantly with an increase in pH. A higher efficiency of energy transfer from tryptophan fluorescence to bixin was observed at higher pH. Thermodynamic parameters and the number of specific binding sites obtained from isothermal titration calorimetry and analytical ultracentrifugation suggested that binding involved mostly hydrophobic interactions for the two specific binding sites. The impacts of pH on binding were correlated to the conformation of β-Lg, the hydrophobic pocket of which becomes more available at higher pH and ionic strength.
β-乳球蛋白（β-Lg）是乳清中的主要蛋白质，辣木红色素是胭脂树中的主要类胡萝卜素，本研究考察了二者在 pH 3.0-10.0 条件下的结合情况。傅里叶变换红外光谱和紫外可见吸收光谱结果表明，二者的结合涉及到复合物的形成。色氨酸荧光猝灭和分析超速离心的数据表明，存在两个特定的结合位点，且结合亲和力随 pH 值的增加而显著增加。在较高 pH 值下，从色氨酸荧光到辣木红色素的能量转移效率更高。等温热滴定和分析超速离心得到的热力学参数和特定结合位点的数量表明，两个特定结合位点的结合主要涉及疏水相互作用。pH 值对结合的影响与β-Lg 的构象有关，在较高 pH 值和离子强度下，β-Lg 的疏水口袋变得更容易接近。
