Patel D J, Woodward C K, Bovey F A
Proc Natl Acad Sci U S A. 1972 Mar;69(3):599-602. doi: 10.1073/pnas.69.3.599.
A resonance (designated a) due to an exchangeable proton titrates (pK(a) = 6.1) between 11.5 and 13 ppm in the nuclear magnetic resonance spectrum of RNase A-0.2 M NaCl in H(2)O at 20 degrees . Comparison with models has permitted assignment to a ring-nitrogen proton of histidine in slow exchange with solvent H(2)O. The pH and temperature-dependent line-width changes of resonance a are analyzed in terms of an exchange between histidine and protonated histidine, without the necessity to invoke any exchange processes associated with protein conformational changes. Several other resonances due to exchangeable protons are observed between 10 and 15 ppm in the nuclear magnetic resonance spectrum of RNase A in H(2)O.
在20摄氏度下，核糖核酸酶A-0.2M氯化钠在水中的核磁共振谱中，由于可交换质子引起的共振（标记为a）在11.5至13ppm之间滴定（pK(a)=6.1）。与模型的比较使得能够将其归属于与溶剂水缓慢交换的组氨酸的环氮质子。共振a的pH和温度依赖性线宽变化根据组氨酸与质子化组氨酸之间的交换进行分析，而无需调用任何与蛋白质构象变化相关的交换过程。在水中核糖核酸酶A的核磁共振谱中，在10至15ppm之间观察到了其他几个由于可交换质子引起的共振。
