一氧化碳和氧气与血红蛋白结合的变构动力学及平衡有所不同。

Allosteric kinetics and equilibria differ for carbon monoxide and oxygen binding to hemoglobin.

作者信息

Zhang N Q, Ferrone F A, Martino A J

机构信息

Department of Physics and Atmospheric Science, Drexel University, Philadelphia, Pennsylvania 19104.

出版信息

Biophys J. 1990 Aug;58(2):333-40. doi: 10.1016/S0006-3495(90)82380-8.

DOI:10.1016/S0006-3495(90)82380-8

PMID:2207241

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC1280975/

Abstract

We have measured the forward and reverse rates of the allosteric transition between R (relaxed) and T (tense) quaternary structures for oxyhemoglobin A from which a single oxygen molecule was removed in pH 7, phosphate buffer, using the method of modulated excitation (Ferrone, F.A., and J.J. Hopfield. 1976. Proc. Natl. Acad. Sci. USA. 73:4497-4501 and Ferrone, F.A., A.J. Martino, and S. Basak. 1985. Biophys. J. 48:269-282). Despite the low quantum yield, which necessitated large light levels and an associated temperature rise, the data was of superior quality to the equivalent experiment with CO as a ligand, permitting comparison between the allosteric behavior of hemoglobin with different ligands. Qualitatively, the T structure is favored more strongly in triligated oxyhemoglobin than triligated carboxyhemoglobin. The rates for the allosteric transition with oxygen bound were essentially temperature independent, whereas for CO both the R----T and T----R rates increased with temperature, having an activation energy of 2.2 and 2.8 kcal, respectively. The R----T rate was higher for O2 than for CO being 3 x 10(3) s-1 vs. 1.6 x 10(3) s-1 for HbCO at 25 degrees C. The T----R rate for HbO2 was only 2 x 10(3) s-1, vs 4.2 x 10(3) s-1 for HbCO, giving an equilibrium constant between the structures greater than unity (L3 = 1.5). The data suggest that there may be some allosteric inequality between the subunits, but do not require (or rule out) ligand binding heterogeneity. The ligand-dependent differences are compatible with stereochemical studies of HbCO and HbO2. However,the large population of T species with three oxygen molecules bound is much greater than predicted by precision equilibrium studies and a generalized Szabo-Karplus model (Lee, A. W., M. Karplus, C. Poyart, and E. Bursaux. 1988. Biochemistry.27:1285-1301) or by the allosteric model of DiCera (Di Cera, E., C. H. Robert, and S. J. Gill. 1987. Biochemistry.26:4003-4008).

摘要

我们使用调制激发法（Ferrone, F.A., 和J.J. Hopfield. 1976. 《美国国家科学院院刊》. 73:4497 - 4501以及Ferrone, F.A., A.J. Martino, 和S. Basak. 1985. 《生物物理学杂志》. 48:269 - 282），测量了在pH 7的磷酸盐缓冲液中，单个氧分子被去除的氧合血红蛋白A从R（松弛）四级结构向T（紧张）四级结构转变的正向和反向速率。尽管量子产率较低，这需要高强度光照并导致相关的温度升高，但所得数据的质量优于以CO作为配体的等效实验，从而能够比较不同配体血红蛋白的变构行为。定性地说，在三配位氧合血红蛋白中，T结构比三配位羧基血红蛋白更受青睐。与氧结合时变构转变的速率基本与温度无关，而对于CO，R→T和T→R速率均随温度升高，其活化能分别为2.2和2.8千卡。在25℃时，O₂的R→T速率高于CO，分别为3×1⁰³ s⁻¹和HbCO的1.6×1⁰³ s⁻¹。HbO₂的T→R速率仅为2×1⁰³ s⁻¹，而HbCO为4.2×1⁰³ s⁻¹，这使得两种结构之间的平衡常数大于1（L3 = 1.5）。数据表明亚基之间可能存在一些变构不均一性，但并不需要（或排除）配体结合的异质性。配体依赖性差异与HbCO和HbO₂的立体化学研究结果相符。然而，结合三个氧分子的T态物种数量远多于精确平衡研究以及广义Szabo - Karplus模型（Lee, A. W., M. Karplus, C. Poyart, 和E. Bursaux. 1988. 《生物化学》. 27:1285 - 1301）或DiCera变构模型（Di Cera, E., C. H. Robert, 和S. J. Gill. 1987. 《生物化学》. 26:4003 - 4008）的预测。