Patel D J, Canuel L L, Bovey F A, Woodward C
Biochim Biophys Acta. 1975 Aug 19;400(2):275-82. doi: 10.1016/0005-2795(75)90182-8.
Several exchangeable resonances, designated a, b, c and d are observed in the 11-14 ppm (from 2,2-dimethyl-2-silapentane-5-sulfonate) region of the proton spectrum of ribonuclease A in water solution. We describe a number of lines of evidence suggesting the assignment of peaks b and c to the N1 and N3 protons of His 48, which occupies an interior position in the protein remote from the active site. This evidence includes the observation that the binding of Cu(II) and 3'-CMP (cytidine 3'-monophosphate) has no effect on these resonances. Further evidence includes pH titration data showing a pKa of approx. 2 for these protons, solvent exchange rates in the native state and with disulfide bridges IV-V and III-VIII cleaved, the observation of the carboxymethylated enzymes CM-His12-RNAase A and CM-His119-RNAase A, and of the modified enzymes Des(1-21)-RNAase A (S-protein) and Des(119-124)-RNAase A.
在核糖核酸酶A水溶液的质子谱11 - 14 ppm（相对于2,2 - 二甲基 - 2 - 硅戊烷 - 5 - 磺酸盐）区域观察到几个可交换的共振峰，分别命名为a、b、c和d。我们描述了一系列证据，表明将峰b和c归属于His 48的N1和N3质子，His 48位于蛋白质内部远离活性位点的位置。这些证据包括观察到Cu(II)和3'-CMP（胞苷3'-单磷酸）的结合对这些共振没有影响。进一步的证据包括pH滴定数据，显示这些质子的pKa约为2，天然状态下以及二硫键IV - V和III - VIII断裂后的溶剂交换率，羧甲基化酶CM - His12 - RNAase A和CM - His119 - RNAase A以及修饰酶Des(1 - 21)-RNAase A（S - 蛋白）和Des(119 - 124)-RNAase A的观察结果。
