Abaturov L V, Nosova N G, Shliapnikov S V, Faĭzullin D A
Mol Biol (Mosk). 2006 Mar-Apr;40(2):326-40.
The rate of the H-D exchange of the peptide NH atoms of the different forms of human Hb was studied at the range of pH 5-10 and temperature 10-63 degrees C by the IR spectroscopy. The pH-dependence of the H-D exchange rate is accordance with the EX2 mechanism. Two pH-dependent conformers of ligand forms of Hb existes at 10-30 degrees C with lower probability of local fluctuations of the alkaline conformer. The difference between two conformers vanishes at 40 degrees C with the appearance of the third conformer with higher probability of local fluctuations. The deoxyHb at 20 degrees C and pH range 6-9 has no pH-dependent conformers and the probability of local fluctuations is considerably reduced in comparison to the acid conformer of ligand Hb. Upon the destabilization of the ligand Hb structure by the pH decreasing to 5.0 at 20 degrees C or the temperature increasing up to 50-60 degrees C at pH 7.1 the global fluctuations of the native structure are intensified providing the H-D exchange of the slowest exchanging NH atoms. The nature of the local and global fluctuations and possible similarity between the two pH-dependent conformers of ligand Hb and its functional R and R2 states revealed by the X-ray analysis and NMR spectroscopy were discussed.
通过红外光谱研究了不同形式的人血红蛋白（Hb）肽链NH原子在pH 5 - 10和温度10 - 63℃范围内的H-D交换速率。H-D交换速率的pH依赖性符合EX2机制。在10 - 30℃时，Hb配体形式存在两种pH依赖性构象体，碱性构象体局部波动的概率较低。在40℃时，两种构象体之间的差异消失，出现了局部波动概率更高的第三种构象体。20℃和pH值范围为6 - 9时的脱氧血红蛋白没有pH依赖性构象体，与配体Hb的酸性构象体相比，局部波动的概率显著降低。在20℃时pH降至5.0或在pH 7.1时温度升至50 - 60℃，导致配体Hb结构不稳定，天然结构的整体波动加剧，使得交换最慢的NH原子发生H-D交换。讨论了局部和整体波动的性质，以及通过X射线分析和核磁共振光谱揭示的配体Hb的两种pH依赖性构象体与其功能性R和R2状态之间可能的相似性。
