Giardina B, Scatena R, Clementi M E, Cerroni L, Nuutinen M, Brix O, Sletten S N, Castagnola M, Condò S G
Institute of Chemistry, Faculty of Medicine, Catholic University, Rome, Italy.
J Mol Biol. 1993 Jan 20;229(2):512-6. doi: 10.1006/jmbi.1993.1050.
Human fetal hemoglobin is known to display, at 20 degrees C, a lower affinity than human adult hemoglobin for oxygen when both proteins are in the absence of organic phosphates. The physiologically important reverse situation is achieved at 37 degrees C upon addition of 2,3-bisphosphoglycerate (DPG), whose lower effect on fetal hemoglobin is related to some amino acid substitutions present in gamma-chains. However, the difference in oxygen affinity observed at 37 degrees C is not solely due to the different modulation power of DPG with respect to adult and fetal hemoglobins. In fact, the results presented here reveal new aspects linked to the interplay of temperature and organic phosphates. In particular, the lower effect of DPG on fetal hemoglobin renders almost identical the oxygen affinity of the two hemoglobins at 20 degrees C, abolishing the difference observed in the absence of the effector. Successively on going from 20 degrees C to 37 degrees C, by virtue of the lower overall heat of oxygenation (delta H) displayed by fetal hemoglobin when in the presence of DPG, adult hemoglobin shows a lower oxygen affinity, as it should if oxygen has to be transferred from maternal to fetal blood.
已知在20摄氏度时，当两种蛋白质都不存在有机磷酸盐时，人类胎儿血红蛋白对氧气的亲和力低于人类成人血红蛋白。在37摄氏度时，加入2,3-二磷酸甘油酸（DPG）可实现生理上重要的相反情况，DPG对胎儿血红蛋白的较低影响与γ链中存在的一些氨基酸取代有关。然而，在37摄氏度时观察到的氧亲和力差异并非仅归因于DPG对成人和胎儿血红蛋白的不同调节能力。事实上，此处呈现的结果揭示了与温度和有机磷酸盐相互作用相关的新方面。特别是，DPG对胎儿血红蛋白的较低影响使得两种血红蛋白在20摄氏度时的氧亲和力几乎相同，消除了在没有效应物时观察到的差异。随后，从20摄氏度升至37摄氏度时，由于胎儿血红蛋白在存在DPG时显示出较低的总体氧合热（ΔH），成人血红蛋白表现出较低的氧亲和力，这是氧气从母体血液转移到胎儿血液时应有的情况。
