Di Cera E, Doyle M L, Gill S J
Department of Chemistry and Biochemistry University of Colorado, Boulder 80309-0215.
J Mol Biol. 1988 Apr 5;200(3):593-9. doi: 10.1016/0022-2836(88)90545-1.
Differential oxygen binding measurements obtained over the pH range 6.95 to 9.10 at 25 degrees C have allowed a detailed description of the alkaline Bohr effect of human hemoglobin Ao. Phenomenological analysis of the data in terms of the Adair equation shows that: (1) the oxygen binding curves are asymmetrical with the population of the triply oxygenated species being negligible throughout the pH range studied: (2) the shape of the oxygen binding curve is affected by pH, especially at low saturation; and (3) the maximum O2-proton linkage is -0.52 mole of proton per mole of oxygen at pH 7.4. A possible molecular mechanism of the Bohr effect is proposed within the framework of an allosteric model which accounts for the low population of triply oxygenated hemoglobin species. At least three Bohr groups are necessary for a quantitative description of the alkaline Bohr effect. Two of these groups titrate in the range of the His146 beta and Vall alpha residues, which have long been identified as the main alkaline Bohr groups, and altogether contribute 84% of the alkaline Bohr effect at physiological pH. A third ionizable group, linked to oxygenation presumably at the beta chains, is implicated and is titrated in a pH range characteristic of a surface histidyl residue.
在25摄氏度下，于pH值6.95至9.10范围内进行的差分氧结合测量，使得能够详细描述人血红蛋白Ao的碱性玻尔效应。根据阿代尔方程对数据进行现象学分析表明：（1）氧结合曲线不对称，在所研究的整个pH范围内，三重氧合物种的数量可忽略不计；（2）氧结合曲线的形状受pH影响，尤其是在低饱和度时；（3）在pH 7.4时，最大O₂-质子键合为每摩尔氧-0.52摩尔质子。在变构模型的框架内提出了玻尔效应的一种可能分子机制，该模型解释了三重氧合血红蛋白物种的低数量。至少需要三个玻尔基团才能对碱性玻尔效应进行定量描述。其中两个基团在His146β和Val1α残基的范围内滴定，这两个残基长期以来一直被确定为主要的碱性玻尔基团，在生理pH下总共贡献了84%的碱性玻尔效应。涉及第三个可电离基团，推测它在β链处与氧合相关，并在表面组氨酸残基特有的pH范围内滴定。
