Reaction of 1-fluoro-2,4-dinitrobenzene with the free alpha chains of human hemoglobin. Evaluation of the pK of the terminal amino group.
Reaction of 1-fluoro-2,4-dinitrobenzene with the free alpha chains of human hemoglobin. Evaluation of the pK of the terminal amino group.
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1-氟-2,4-二硝基苯与人血红蛋白的游离 α 链的反应。
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发表时间：
1971
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通讯作者：
E. Bucci
中科院分区：
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作者：
S. de Bruin;E. Bucci
摘要研究了巯基形式α链分离的1-氟-2,4-二硝基苯与对汞苯甲酸酯（PMB）的反应。通过对353 nm处的吸光度变化的动力学测量，计算出该基团的pK为7.30。与ph无关的反应常数估计为0.282 m-1 sec-1。比较未处理的α链与末端缬氨酸取代的α链（α pmbdnp）的质子结合行为，计算出该组的pK为7.4。组氨酸似乎没有二硝基苯化。然而，从与1-氟-2,4-二硝基苯反应时质子的释放速度来看，我们得出结论，它们确实与试剂相互作用，但没有形成稳定的衍生物。这些残基的pK为6.85，反应常数与ph无关，为0.023 m-1 sec-1。通过对α pmbdnp和β链以巯基形式与对汞苯甲酸盐混合的氧平衡研究，我们计算出Hill参数n的值为1.35。该混合物的s20，w为4.95，而当α链未二硝基苯化时，它接近2.5 （Antonini et al.， J. Mol. Biol.）。， 17,29(1966))，表明二硝基苯基化强烈地促进了四聚体的形成。与血红蛋白通常使用的v = 0.749相比，这种高沉降值与部分比体积v = 0.731相一致（Svedberg和Pedersen，超离心机，牛津大学出版社，纽约，1940）。
Abstract The reaction of 1-fluoro-2,4-dinitrobenzene with isolated α chains in their mercaptide form with p-mercuribenzoate (PMB) was studied. From kinetic measurements with the change in absorbance at 353 nm upon substitution of the terminal valine, the pK of this group was calculated to be 7.30. The pH-independent reaction constant was estimated to be 0.282 m-1 sec-1. Comparing the proton-binding behavior of untreated α chains with that of the chains substituted in the terminal valine (αpmbDNP) the pK of this group was calculated to be 7.4. Histidines did not appear to be dinitrophenylated. However, from the rate of liberation of protons upon the reaction of the chains with 1-fluoro-2,4-dinitrobenzene we concluded that they do interact with the reagent without forming a stable derivative. A pK of 6.85 and a pH-independent reaction constant of 0.023 m-1 sec-1 per individual group was calculated for these residues. From oxygen equilibrium studies on a mixture in equal amount of αpmbDNP and β chains in their mercaptide form with p-mercuribenzoate we calculated a value of 1.35 for the Hill parameter n. The s20,w of this mixture was 4.95 while it is near 2.5 when the α chains are not dinitrophenylated (Antonini et al., J. Mol. Biol., 17, 29 (1966)), indicating that the dinitrophenylation strongly favors the formation of tetramers. This high sedimentation value is consistent with a partial specific volume v = 0.731, as compared to v = 0.749 commonly used for hemoglobin (Svedberg and Pedersen, The ultracentrifuge, Oxford University Press, New York, 1940).