Mathematical models for interacting groups in nuclear magnetic resonance titration curves.
Mathematical models for interacting groups in nuclear magnetic resonance titration curves.
复制标题
核磁共振滴定曲线中相互作用基团的数学模型。
DOI：
10.1021/bi00754a010
复制
发表时间：
1972
期刊：
影响因子：
2.9
通讯作者：
A. Schechter
中科院分区：
文献类型：
--
作者：
R. Shrager;J. Cohen;S. Heller;D. Sachs;A. Schechter
Richard I. Shrager, Jack S. Cohen, Stephen R. Heller, David H. Sachs和Alan N. Schechter摘要：建立了用于解释化学位移与pH的核磁共振滴定曲线的数学模型，并强调了两个相互作用的滴定基团的情况。用计算机曲线拟合的方法对l-组氨酸、tv -乙酰- l-组氨酸、l-组氨酸甲酯和几种l-组氨酸二肽的咪唑C-2和C-4质子共振数据进行了拟合。由于邻近的滴定氨基和羧基的影响，在这些滴定曲线中观察到弯曲。曲线拟合程序提供了咪唑和相互作用的滴定基团的电离常数的精确值，即使当pK值足够接近，弯曲合并产生不对称曲线。将这些方法应用于l-组氨酸- l-组氨酸的滴定曲线表明，在其中一条曲线的高pH区所注意到的不对称是由于相邻氨基的影响，而不是两个咪唑环之间的相互作用。L - roton磁共振波谱已被用于测定多肽和蛋白质中单个组氨酸残基的咪唑环的pK值（Bradbury和Scheraga, 1966； Roberts等人，1969;Cohen, 1969, 1971）。所获得的值提供了有关这些残基的局部环境的信息，并可用于研究配体和其他摄动物的影响（Meadows et al., 1969; Ru-terjans and Witzel, 1969）。在一些情况下，咪唑质子化学位移随pH值的变化曲线偏离了描述简单质子缔合平衡的理论曲线（Ruterjans and Witzel, 1969; Cohen et al., 1970a; King and Bradbury, 1971; Ruterjans and Pongs, 1971）。这些偏差表示咪唑残基和分子内其他带电基团之间的相互作用。
Richard I. Shrager, Jack S. Cohen, Stephen R. Heller, David H. Sachs, and Alan N. Schechter abstract: Mathematical models were developed for the interpretation of nuclear magnetic resonance titration curves of chemical shift vs. pH with emphasis on the case of two interacting titrating groups. The equations were applied by means of computer curvé fitting to data obtained for the imidazole C-2 and C-4 proton resonances of L-histidine, TV-acetyl-L-histidine, L-histidine methyl ester, and several L-histidine dipeptides. Inflections are observed in these titration curves due to the effects of the neighboring titrating amino and car-boxyl groups. The curve-fitting procedure provided accurate values for the ionization constants of the imidazole and the interacting titrating groups, even when the pK values were sufficiently close that the inflections hadmerged to produce an asymmetric curve. Application of these procedures to the titration curves of L-histidyl-L-histidine indicated that the asymmetry noted in the high pH region of one of the curves is due to the effect of an adjacent amino group and not to an interaction between the two imidazole rings.L roton magnetic resonance spectroscopy has been used to determine the pK values of the imidazole rings of individual histidine residues in peptides and proteins (Bradbury and Scheraga, 1966; Roberts et al., 1969; Cohen, 1969, 1971). The values obtained give information about the local environ-ments of these residues, and may be used tostudy the effects of ligands and other perturbants (Meadows et al., 1969; Ru-terjans and Witzel, 1969). In several cases the titration curves of imidazole proton chemical shift as a function of pH have deviated from the theoretical curve describing a simple proton association equilibrium (Ruterjans and Witzel, 1969; Cohen et al., 1970a; King and Bradbury, 1971; Ruterjans and Pongs, 1971). These deviations represent interactions between the imidazole residues and other charged groups within the mole-cule.