Huang Y, Doyle M L, Ackers G K
Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Biophys J. 1996 Oct;71(4):2094-105. doi: 10.1016/S0006-3495(96)79408-0.
Hemoglobin tetramers [Zn/FeO(2)] containing oxygenated subunits (FeO(2)), in combination with unligated subunits containing zinc-substituted hemes (Zn), were analyzed to determine their contributions to the cooperativity of oxygen binding at the Fe sites. Energetic consequences of possible perturbation by zinc substitution were evaluated in all combinations of unligated Zn/Fe hybrid tetramers. A general thermodynamic strategy that corrects for the energetic effects of substituting a second metal for Fe showed the perturbations of Zn substitution to be negligible. This permitted cooperativity parameters of the native Fe/FeO(2) intermediates to be calculated from data on the corresponding Zn/FeO(2) molecules. These parameters, determined explicitly for all eight oxygen-binding intermediates (Fe/FeO(2)), were found to be identical to those predicted earlier from analyzing the O(2) binding data of normal hemoglobin according to the "molecular code" of hemoglobin allostery. The cooperativity parameters determined for this system showed the same distribution pattern found previously for five other oxygen analog systems (Fe/FeCN, FE/Mn(3+), Co/FECO, Co/FeCN, and Fe/FeCO).
对含有氧合亚基(FeO₂)的血红蛋白四聚体[Zn/FeO₂]与含有锌取代血红素(Zn)的未结合配体的亚基相结合的情况进行了分析,以确定它们对铁位点上氧结合协同性的贡献。在未结合配体的Zn/Fe杂合四聚体的所有组合中评估了锌取代可能产生的扰动的能量后果。一种校正用第二种金属取代铁的能量效应的通用热力学策略表明,锌取代的扰动可忽略不计。这使得能够根据相应的Zn/FeO₂分子的数据计算天然Fe/FeO₂中间体的协同性参数。明确确定的所有八种氧结合中间体(Fe/FeO₂)的这些参数,与先前根据血红蛋白变构的“分子密码”分析正常血红蛋白的O₂结合数据所预测的参数相同。为该系统确定的协同性参数显示出与之前其他五个氧类似物系统(Fe/FeCN、FE/Mn³⁺、Co/FECO、Co/FeCN和Fe/FeCO)相同的分布模式。