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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Kinetic gating of the proton pump in cytochrome c oxidase
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Kinetic gating of the proton pump in cytochrome c oxidase

机译：质子泵在细胞色素c氧化酶中的动力学门控

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摘要

Cytochrome c oxidase (CcO), the terminal enzyme of the respiratory chain, reduces oxygen to water and uses the released energy to pump protons across a membrane. Here, we use kinetic master equations to explore the energetic and kinetic control of proton pumping in CcO. We construct models consistent with thermodynamic principles, the structure of CcO, experimentally known proton affinities, and equilibrium constants of intermediate reactions. The resulting models are found to capture key properties of CcO, including the midpoint redox potentials of the metal centers and the electron transfer rates. We find that coarse-grained models with two proton sites and one electron site can pump one proton per electron against membrane potentials exceeding 100 mV. The high pumping efficiency of these models requires strong electrostatic couplings between the proton loading (pump) site and the electron site (heme a), and kinetic gating of the internal proton transfer. Gating is achieved by enhancing the rate of proton transfer from the conserved Glu-242 to the pump site on reduction of heme a, consistent with the predictions of the water-gated model of proton pumping. The model also accounts for the phenotype of D-channel mutations associated with loss of pumping but retained turnover. The fundamental mechanism identified here for the efficient conversion of chemical energy into an electrochemical potential should prove relevant also for other molecular machines and novel fuel-cell designs.
机译：细胞色素c氧化酶（CcO）是呼吸链的末端酶，可将氧气还原为水，并利用释放出的能量将质子泵过膜。在这里，我们使用动力学主方程来探索CcO中质子泵浦的能量和动力学控制。我们构建符合热力学原理，CcO的结构，实验已知的质子亲和力和中间反应平衡常数的模型。发现所得模型捕获了CcO的关键特性，包括金属中心的中点氧化还原电势和电子传输速率。我们发现具有两个质子位点和一个电子位点的粗粒度模型可以针对超过100 mV的膜电位向每个电子泵送一个质子。这些模型的高泵浦效率要求质子加载（泵）位和电子位（血红素a）之间具有强的静电耦合，并且需要内部质子传递的动力学门控。通过提高血红素a降低时从保守的Glu-242到质子转移到泵浦位置的质子转移速率来实现门控，这与质子泵浦水控模型的预测一致。该模型还说明了与泵浦丧失但保留营业额相关的D通道突变的表型。此处确定的将化学能有效转化为电化学势的基本机制也应证明与其他分子机器和新颖的燃料电池设计有关。

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