Matthews C R, Westmoreland D G
Biochemistry. 1975 Oct 7;14(20):4532-8. doi: 10.1021/bi00691a031.
A proton nuclear magnetic resonance study of the four histidine residues of thermally unfolded ribonuclease A has provided evidence that two of the residues are in regions of residual structure, whereas the other two are freely exposed to solvent. Histidine-48 and, tentatively, histidine-105 occupy an environment at 69 degrees characterized by residual structure and display a pK value of 5.75 and a spin-lattice relaxation time of about 0.8 sec at pH 5.5. Histidine-12 and, tentatively, histidine-119 are in an environment at 69 degrees which is freely accessible to solvent and show a pK value of 5.96 and a spin-lattice relaxation time of about 1.1 sec at pH 5.5.
对热变性核糖核酸酶A的四个组氨酸残基进行的质子核磁共振研究提供了证据，表明其中两个残基处于残余结构区域，而另外两个则自由暴露于溶剂中。组氨酸-48以及初步确定的组氨酸-105在69摄氏度时所处环境具有残余结构，在pH 5.5时pK值为5.75，自旋晶格弛豫时间约为0.8秒。组氨酸-12以及初步确定的组氨酸-119在69摄氏度时所处环境可被溶剂自由接触，在pH 5.5时pK值为5.96，自旋晶格弛豫时间约为1.1秒。
