Ferrone F A, Martino A J, Basak S
Biophys J. 1985 Aug;48(2):269-82. doi: 10.1016/S0006-3495(85)83780-2.
We have used the method of modulated excitation (Ferrone, F.A., and J.J. Hopfield, 1976, Proc. Natl. Acad. Sci. USA. 73:4497-4501), with an improved apparatus and a revised analytical procedure, to measure the rate of conformational change between the oxy (R) and deoxy (T) conformations of triligated carboxy-hemoglobin A at pH 6.5 and 7.0. We have found the rates to be kRT = 1.2 X 10(3) s-1 and kTR = 3.5 X 10(3) s-1 for pH 6.5, while for pH 7.0, kRT = 1.0 X 10(3) s-1, and kTR = 3.0 X 10(3) s-1. The value for L3, the equilibrium constant between conformations, was virtually unchanged between pH 6.5 and 7.0. While the rates measured here differ from those obtained in the original use of this method, these new rates are fully consistent with the original data when analyzed by the revised procedures presented here. When taken with other kinetic and equilibrium data, our measurements suggest that the transition state between structures is dominated by the behavior of the T quaternary structure. Finally, a spectral feature near the HbCO Soret peak has been observed that we ascribe to an allosteric perturbation of the spectra of the liganded hemes.
我们采用调制激发方法（费罗内，F.A.，和J.J.霍普菲尔德，1976年，《美国国家科学院院刊》。73:4497 - 4501），使用改进的仪器和修订的分析程序，来测量在pH 6.5和7.0条件下三配位羧基血红蛋白A的氧合（R）构象与脱氧（T）构象之间的构象变化速率。我们发现，在pH 6.5时，速率为kRT = 1.2×10³ s⁻¹，kTR = 3.5×10³ s⁻¹；而在pH 7.0时，kRT = 1.0×10³ s⁻¹，kTR = 3.0×10³ s⁻¹。构象之间的平衡常数L3的值在pH 6.5和7.0之间几乎没有变化。虽然这里测量的速率与最初使用该方法时获得的速率不同，但当按照这里提出的修订程序进行分析时，这些新速率与原始数据完全一致。结合其他动力学和平衡数据来看，我们的测量结果表明，结构之间的过渡态主要由T四级结构的行为主导。最后，在HbCO Soret峰附近观察到一个光谱特征，我们将其归因于配位血红素光谱的变构扰动。
