Carey J, Uhlenbeck O C
Biochemistry. 1983 May 24;22(11):2610-5. doi: 10.1021/bi00280a003.
A filter retention assay is used to examine the kinetic and equilibrium properties of the interaction between phage R17 coat protein and its 21-nucleotide RNA binding site. The kinetics of the reaction are consistent with the equilibrium association constant and indicate a diffusion-controlled reaction. The temperature dependence of Ka gives delta H = -19 kcal/mol. This large favorable delta H is partially offset by a delta S = -30 cal mol-1 deg-1 to give a delta G = -11 kcal/mol at 2 degrees C in 0.19 M salt. The binding reaction has a pH optimum centered around pH 8.5, but pH has no effect on delta H. While the interaction is insensitive to the type of monovalent cation, the affinity decreases with the lyotropic series among monovalent anions. The ionic strength dependence of Ka reveals that ionic contacts contribute to the interaction. Most of the binding free energy, however, is a result of nonelectrostatic interactions.
一种滤膜滞留测定法被用于检测噬菌体R17外壳蛋白与其21核苷酸RNA结合位点之间相互作用的动力学和平衡特性。该反应的动力学与平衡缔合常数一致，表明这是一个扩散控制反应。Ka的温度依赖性给出ΔH = -19千卡/摩尔。这个较大的有利ΔH被ΔS = -30卡·摩尔⁻¹·℃⁻¹部分抵消，从而在2℃、0.19 M盐浓度下得到ΔG = -11千卡/摩尔。结合反应的最适pH值集中在pH 8.5左右，但pH对ΔH没有影响。虽然这种相互作用对单价阳离子的类型不敏感，但亲和力随着单价阴离子的感胶离子序而降低。Ka对离子强度的依赖性表明离子接触对这种相互作用有贡献。然而，大部分结合自由能是非静电相互作用的结果。
