Okonjo Kehinde Onwochei
Department of Chemistry, University of Ibadan, Niger Road, Ibadan, Nigeria.
Biophys Chem. 2017 Sep;228:87-97. doi: 10.1016/j.bpc.2017.07.006. Epub 2017 Jul 15.
As a prelude to separating tertiary from quaternary structure contributions to the Bohr effect, we employed the Wyman equation to analyze Bohr data for human hemoglobin to which 2,3-bisphosphoglycerate, 2,3-BPG, is bound. Changes in the pKs of the histidine Bohr groups result in a net reduction of their contributions to the Bohr effect at pH 7.4 compared to their contributions in stripped hemoglobin. The non-histidine 2,3-BPG binding groups - the β-chain terminal amino group and Lys82β - make negative and positive contributions, respectively, to the Bohr effect. The final result is that the Bohr effect at physiological pH is higher for 2,3-BPG bound compared to stripped hemoglobin. Contributions linked to His2β, His77β and His143β enable us to separate tertiary from quaternary Bohr contributions in stripped and in 2,3-BPG bound hemoglobin. Both contributions serve to make the Bohr effect for 2,3-BPG bound hemoglobin higher than for stripped hemoglobin at physiological pH.
作为区分三级结构和四级结构对玻尔效应贡献的前奏，我们使用怀曼方程来分析人血红蛋白的玻尔数据，该血红蛋白结合了2,3-二磷酸甘油酸（2,3-BPG）。与去辅基血红蛋白中的贡献相比，组氨酸玻尔基团的pK值变化导致它们在pH 7.4时对玻尔效应的贡献净减少。非组氨酸的2,3-BPG结合基团——β链末端氨基和Lys82β——分别对玻尔效应产生负贡献和正贡献。最终结果是，与去辅基血红蛋白相比，结合2,3-BPG的血红蛋白在生理pH下的玻尔效应更高。与His2β、His77β和His143β相关的贡献使我们能够区分去辅基血红蛋白和结合2,3-BPG的血红蛋白中三级结构和四级结构对玻尔效应的贡献。在生理pH下，这两种贡献都使得结合2,3-BPG的血红蛋白的玻尔效应高于去辅基血红蛋白。
