Kolb D A, Weber G
Biochemistry. 1975 Oct 7;14(20):4476-81. doi: 10.1021/bi00691a021.
When a ligand X is multiply bound to energetically identical, noninteracting sites of a protein, cooperative binding of this ligand can be induced by the presence of a second ligand Y. This effect should appear whenever multiple interactions exist between the bound X and Y ligands, and vanish when the concentration of Y is made sufficiently large to ensure Y saturation at all concentrations of X. These predictions have been verified for the binding of 8-anilino-1-naphthalenesulfonate to serum albumin, when Y, the effector ion, is 3,5-dihydroxybenzoate. In the presence of 2mM dihydroxybenzoate, the Hill coefficient for anilinonaphthalenesulfonate binding rose steadily from 1 to 1.5 as the number of molecules of ligand bound increased from 1 to 3.3 per albumin molecule. The theory of interactions between isolated ligands, applied in the previous paper (D. A. Kolb and G. Weber (1975), Biochemistry, preceding paper in this issue), is extended to cases of multiple interactions, and applied here to show that the experimental results are tolerably well reproduced for a model in which four anilinonaphthalensulfonate molecules are homogeneously coupled to four molecules of dihydroxybenzoate by free energies of 3.0 and 3.5 thermal units.
当配体X多重结合于蛋白质的能量相同、互不作用的位点时，第二种配体Y的存在可诱导该配体发生协同结合。只要结合的X和Y配体之间存在多重相互作用，这种效应就会出现，而当Y的浓度足够高以确保在所有X浓度下Y均饱和时，该效应就会消失。当效应离子Y为3,5 - 二羟基苯甲酸时，8 - 苯胺基 - 1 - 萘磺酸盐与血清白蛋白的结合已证实了这些预测。在存在2mM二羟基苯甲酸的情况下，随着每分子白蛋白结合的配体分子数从1增加到3.3，苯胺基萘磺酸盐结合的希尔系数从1稳步上升至1.5。在前一篇论文（D. A. 科尔布和G. 韦伯（1975年），《生物化学》，本期前一篇论文）中应用的孤立配体间相互作用理论，扩展至多重相互作用的情况，并在此处应用以表明，对于一个模型而言，实验结果能够得到较好的重现，在该模型中，四个苯胺基萘磺酸盐分子通过3.0和3.5个热单位的自由能与四个二羟基苯甲酸分子均匀偶联。
