Spot hemoglobin. Studies on the Root effect hemoglobin of a marine teleost.
Spot hemoglobin. Studies on the Root effect hemoglobin of a marine teleost.
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斑点血红蛋白。
DOI：
10.1016/s0021-9258(17)33629-3
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发表时间：
1976
期刊：
影响因子：
--
通讯作者：
J. Bonaventura
中科院分区：
文献类型：
--
作者：
C. Bonaventura;B. Sullivan;J. Bonaventura
这种斑点鱼，Leiostomus xanthrus，有一个单一的四聚体血红蛋白。结构研究表明存在α-和β-样链，分别具有-Arg和-TYR-His的COOH末端序列，与人血红蛋白中发现的相同。斑点血红蛋白具有根效应：一种异向控制机制，如玻尔效应，但在O2和CO结合的平衡和动力学中具有更极端的pH依赖性。根效应似乎是一种分子适应，在pH值和阴离子敏感的血红蛋白可以帮助鱼类实现中性浮力，促进O2输送到鱼鳔。“开”和“关”过程的动力学变化导致斑点血红蛋白在低pH下的配体亲和力大大降低。在低pH下配体结合的时间过程是双相的和波长依赖的，表明pH对α-和β-样链的不同影响。配体结合曲线形状随pH的变化可以解释为低（T）和高（R）亲和力构象之间的质子依赖性转变。然而，这可能不是唯一的机制，因为不同的pH值对两种类型的链的影响也可能有助于观察到的pH值依赖性。
The Spot, Leiostomus xanthrus, has a single tetrameric hemoglobin. Structural studies indicate the presence of alpha- and beta-like chains with COOH-terminal sequences of --Arg and --TYR-His, respectively, the same as is found in human hemoglobin. Spot hemoglobin possesses a Root effect: a heterotropic control mechanism like the Bohr effect but with more extreme pH dependence in the equilibria and kinetics of O2 and CO binding. The Root effect seems to be a molecular adaptation, in that pH- and anion-sensitive hemoglobins may help fish achieve neutral buoyancy by facilitating O2 delivery to the swim bladder. Changes in the kinetics of both "on" and "off" processes contribute to the greatly decreased ligand affinity of Spot hemoglobin at low pH. The time course ofligand combination at low pH is biphasic and wavelength dependent, suggesting a differential effect of pH on the alpha- and beta-like chains. The change in the shape of the ligand-binding curve with pH may be interpreted in terms of a proton-dependent transition between low (T) and high (R) affinity conformations. However, this may not be the only mechanism, since differential pH effects on the two types of chains may also contribute to the observed pH dependence.