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首页> 外文期刊>Biochemistry >Control of electron delivery to the oxygen reduction site of cytochrome c oxidase: a role for protons.
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Control of electron delivery to the oxygen reduction site of cytochrome c oxidase: a role for protons.

机译：控制电子向细胞色素C氧化酶的氧还原位点的传递：质子的作用。

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We have studied the reaction of oxidized "pulsed" cytochrome c oxidase with reduced cytochrome c and with ruthenium(II) hexaammine using stopped-flow mixing. The rate of reduction of Fea3 (the oxygen-binding heme) is not a linear function of the population of reduced Fea (the low-spin heme), as would be expected if electron transfer between these sites is rate-limiting. Instead, the rate can be increased significantly by increasing the driving force of the reductant (lowering of Eh) even after Fea is almost completely reduced. Reduction of Fea3 becomes slower as the pH is raised, and consumption of protons can be seen simultaneously with electron entry into Fea3. Both the reduction of Fea3 and the proton uptake are biphasic. To explain these findings, we propose a model in which (1) intramolecular heme-heme electron transfer is fast, and has an essentially constant rate; (2) when reduction begins, the midpoint potentials of Fea3 and CuB are initially low, and only a small fraction of these centers become reduced; and (3) this reduced population is then stabilized by the uptake of protons. Thus, net reduction of Fea3 and CuB is controlled by the amount of the low-potential population which becomes reduced together with the rate of proton uptake by this reduced low-potential species. Important consequences of this mechanism for the function of the enzyme and for the respiratory chain as a whole are discussed.
机译：我们已经研究了氧化的“脉冲”细胞色素C氧化酶与还原的细胞色素C以及钌（II）六氨合胺的反应，采用了限流混合技术。 Fea3（与氧结合的血红素）的还原速率与还原的Fea（低自旋血红素）的数量不是线性函数，如果这些位点之间的电子传递受到速率限制，这是可以预期的。取而代之的是，即使在Fea几乎完全降低之后，也可以通过增加还原剂的驱动力（降低Eh）来显着提高速率。随着pH的升高，Fea3的还原变慢，并且在电子进入Fea3的同时可以看到质子的消耗。 Fea3的减少和质子的吸收都是双相的。为了解释这些发现，我们提出了一个模型，其中：（1）分子内血红素-血红素电子转移快速，并且具有基本恒定的速率; （2）当还原开始时，Fea3和CuB的中点电位开始较低，这些中心中只有一小部分被还原; （3）然后通过质子的吸收来稳定该减少的种群。因此，Fea3和CuB的净还原量由低电势族的数量控制，该数量降低了，而该还原的低电势物种的质子吸收率也降低了。讨论了这种机制对酶的功能以及整个呼吸链的重要影响。

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