【4.1.2】波尔效应

波尔效应是指H+和CO2促进Hb释放O2的现象。产生波尔效应的原因是H+和CO2能够与Hb特定位点结合，而促进Hb从R态转变为T态。与H+引发的波尔效应相关的基团有：a亚基的N-端氨基、a亚基的His122咪唑基以及b亚基的His146咪唑基。这三个基团在Hb处于T态的时候都是高度质子化的，而当氧气与Hb结合以后，质子发生解离。如果溶液中的pH降低，将有利于这三个基团处于质子化状态，从而稳定T态，抑制氧气的结合。用反应式来表示，即为：Hb + O2 Hb(O2)4 + nH+。显然pH下降，即H+浓度升高，会使反应平衡向左移动，这时有利于Hb释放结合的氧气。

1. 质子和二氧化碳浓度的上升可促进血红蛋白释放氧气(H+ and CO2 promote the release of O2 from Hb).
2. 质子诱发波尔效应的原因是血红蛋白结合氧气的时候，事实上发生了反应，有 若干个质子释放出来:O2 + Hb ↔ Hb(O2)4 + xH+，质子浓度的上升可使反应平 衡向左移动，因而有利于血红蛋白释放氧气(The reason that protons induce the Bohr effect is that when O2 binds to Hb, a reaction will actually happen: O2 + Hb ↔ Hb(O2)4 + xH+, in which Hb releases a couple of protons. So as the proton concentration increases, the reaction equilibrium will shift from right to left side, thus causing disassociation of O2 from Hb).
3. CO2诱发波尔效应的机制有两个:一是通过质子起作用，二是通过共价修饰血 红蛋白N端的氨基，致使αβ亚基之间形成一个盐键，有助于稳定T态( CO2 induces the Bohr effect by two mechanisms: one is by H+ and the other is by modifying the N-terminal amino group covalently on Hb. Formation of carbamates on Hb results in the formation of salt bridges between the α and β chains, which stabilizes Hb in the T state and thus lowers the O2 affinity of Hb).
4. 波尔效应的好处是使得血红蛋白更适合充当氧气的运输者(The advantage carried by Bohr effect is to make HbA more suitable for being a O2 carrier).

参考资料

• 南京大学 杨荣武老师 《结构生物学》课件