Shibayama N, Morimoto H, Saigo S
Department of Physics, Jichi Medical School, Minamikawachi, Tochigi, Japan.
Biochemistry. 1997 Apr 15;36(15):4375-81. doi: 10.1021/bi970009m.
It has been reported that hybridization of the equimolar mixture of cyanomethemoglobin and deoxyhemoglobin through dimer exchange reaction results in establishment of an approximately binomial (1:2:1) equilibrium distribution of these parental hemoglobins and their hybrid molecule, (alpha+CN-beta+CN-)(alpha beta), within several days under anaerobic conditions at pH 7.4, 21.5 degrees C, leading to a hyper (i.e., about 170 times) thermodynamic stability of (alpha+CN-beta+CN-)(alpha beta) relative to the stability of the other diliganded species at pH 7.4, 21.5 degrees C [Daugherty, M. A., Shea, M. A., Johnson, J. A., LiCata, V. J., Turner, G. J., & Ackers, G. K. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 1110-1114]. To examine whether the published "binomiality" for this deoxy-cyanomet hybrid system really reflects the thermodynamic stability of (alpha+CN-beta+CN-)(alpha beta), we used a binomial (1:2:1) equilibrium distribution of the equimolar mixture of cyanomethemoglobin and fully oxygenated hemoglobin as a starting condition, and then this system was rapidly deoxygenated. We found that the relative population of the hybrid was reduced to 8.6% of the total upon deoxygenation. It was also found that the hybridization experiment under anaerobic conditions was not allowed to continue for a long time due to a valency exchange reaction between deoxy and cyanomet derivatives. For instance, a 48 h incubation resulted in the oxidation of 44% of Fe2+ to Fe3+ hemes in the original deoxyhemoglobin and the reduction of 42% of Fe3+ to Fe2+ hemes in the original cyanomethemoglobin. These results suggest that a real distribution of the deoxy-cyanomet hybrid system at equilibrium is fairly far from 1:2:1 (binomial distribution), and the thermodynamic stability of (alpha+CN-beta+CN-)(alpha beta) is less than one-tenth of the hyperstability previously reported. In addition, most of the previous results on deoxy-cyanomet valency hybrids placed under long anaerobic conditions should be subject to reexamination due to possible valency exchange reactions.
据报道，在pH 7.4、21.5℃的厌氧条件下，氰化高铁血红蛋白和脱氧血红蛋白的等摩尔混合物通过二聚体交换反应进行杂交，会在数天内建立起这些亲本血红蛋白及其杂交分子（α + CN - β + CN -）（αβ）的近似二项式（1:2:1）平衡分布，这导致（α + CN - β + CN -）（αβ）相对于pH 7.4、21.5℃下其他双配体物种的稳定性具有超（即约170倍）热力学稳定性[多尔蒂，M. A.，谢伊，M. A.，约翰逊，J. A.，利卡塔，V. J.，特纳，G. J.，& 阿克斯，G. K.（1991年）《美国国家科学院院刊》88，1110 - 1114]。为了检验已发表的该脱氧 - 氰化高铁杂交系统的“二项式分布”是否真的反映了（α + CN - β + CN -）（αβ）的热力学稳定性，我们以氰化高铁血红蛋白和完全氧合血红蛋白的等摩尔混合物的二项式（1:2:1）平衡分布作为起始条件，然后将该系统快速脱氧。我们发现脱氧后杂交体的相对含量降至总量的8.6%。还发现由于脱氧和氰化高铁衍生物之间的价态交换反应，厌氧条件下的杂交实验不能长时间持续进行。例如，48小时的孵育导致原始脱氧血红蛋白中44%的Fe2 + 血红素氧化为Fe3 + 血红素，原始氰化高铁血红蛋白中42%的Fe3 + 血红素还原为Fe2 + 血红素。这些结果表明，脱氧 - 氰化高铁杂交系统在平衡时的实际分布与1:2:1（二项式分布）相差甚远，并且（α + CN - β + CN -）（αβ）的热力学稳定性小于先前报道的超稳定性的十分之一。此外，由于可能的价态交换反应，之前在长时间厌氧条件下对脱氧 - 氰化高铁价态杂交体的大多数结果都应重新审视。
