Functional and spectroscopic characterization of half-liganded iron-zinc hybrid hemoglobin: evidence for conformational plasticity within the T state.
Functional and spectroscopic characterization of half-liganded iron-zinc hybrid hemoglobin: evidence for conformational plasticity within the T state.
复制标题
半配体铁锌杂化血红蛋白的功能和光谱表征：T 态内构象可塑性的证据。
DOI：
10.1021/bi020648j
复制
发表时间：
2003
期刊：
影响因子：
--
通讯作者：
Friedman,JoelM
中科院分区：
文献类型：
--
作者：
Samuni,Uri;Juszczak,Laura;Dantsker,David;Khan,Imran;Friedman,AdamJ;Perez-Gonzalez-de-Apodaca,Jose;Bruno,Stefano;Hui,HildaL;Colby,JudithE;Karasik,Ellen;Kwiatkowski,LauraD;Mozzarelli,Andrea;Noble,Robert;Friedman,JoelM
氧结合血红蛋白固定在T状态无论是通过结晶或封装在硅胶显然是不合作的。然而，协同性可能被α和β亚基的不同氧亲和力所掩盖。金属混合血红蛋白中的非铁金属不与氧结合，这为分别测定α和β血红素的氧亲和力提供了机会。以前的研究已经表征了α（Ni 2+）2 β（Fe 2+）2晶体的氧结合。本文测定了聚乙二醇溶液中生长的α（Fe ~（2+））_2 β（Ni ~（2+））_2晶体的三维结构和氧结合。用单晶显微分光光度法记录了不同氧分压下平行于B或c晶轴偏振的光的偏振吸收光谱。沿着B和c晶轴的50%饱和度（p50 s）下的氧压分别为95 ± 3和87 ± 4托，并且相应的希尔系数为0.96 ± 0.06和0.90 ± 0.03。结合曲线的分析，考虑到不同的投影α血红素沿着的光学方向，表明α1血红素的氧亲和力是1.3倍低于α2血红素。检查的3D结构表明，这种不等价性可能会出现从包装内的单斜晶格的Hb四聚体的相互作用。α（Ni ~（2+））_2 β（Fe ~（2+））_2晶体的β亚基也存在类似的不等价性。α亚基（p50 = 91 Torr）的平均氧亲和力比β亚基（p50 = 110 Torr）高约1.2倍。在缺乏协同性的情况下，这种异质性产生了血红蛋白A的氧结合曲线，希尔系数为0.999。由于血红蛋白A晶体的结合曲线表现出希尔系数非常接近统一，这些研究结果表明，T-状态血红蛋白的氧结合是不合作的，与莫诺，怀曼，和Changeux模型。
Oxygen binding by hemoglobin fixed in the T state either by crystallization or by encapsulation in silica gels is apparently noncooperative. However, cooperativity might be masked by different oxygen affinities of α and β subunits. Metal hybrid hemoglobins, where the noniron metal does not bind oxygen, provide the opportunity to determine the oxygen affinities of α and β hemes separately. Previous studies have characterized the oxygen binding by α(Ni2+)2 β(Fe2+)2 crystals. Here, we have determined the three-dimensional (3D) structure and oxygen binding of α(Fe2+)2 β(Ni2+)2 crystals grown from polyethylene glycol solutions. Polarized absorption spectra were recorded at different oxygen pressures with light polarized parallel either to the b or c crystal axis by single crystal microspectrophotometry. The oxygen pressures at 50% saturation (p50s) are 95 ± 3 and 87 ± 4 Torr along the b and c crystal axes, respectively, and the corresponding Hill coefficients are 0.96 ± 0.06 and 0.90 ± 0.03. Analysis of the binding curves, taking into account the different projections of the α hemes along the optical directions, indicates that the oxygen affinity of α1 hemes is 1.3-fold lower than α2 hemes. Inspection of the 3D structure suggests that this inequivalence may arise from packing interactions of the Hb tetramer within the monoclinic crystal lattice. A similar inequivalence was found for the β subunits of α(Ni2+)2 β(Fe2+)2 crystals. The average oxygen affinity of the α subunits (p50 = 91 Torr) is about 1.2-fold higher than the β subunits (p50 = 110 Torr). In the absence of cooperativity, this heterogeneity yields an oxygen binding curve of Hb A with a Hill coefficient of 0.999. Since the binding curves of Hb A crystals exhibit a Hill coefficient very close to unity, these findings indicate that oxygen binding by T-state hemoglobin is noncooperative, in keeping with the Monod, Wyman, and Changeux model.