Electron-proton interactions in terminal oxidases
Electron-proton interactions in terminal oxidases
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DOI：
10.1016/s0005-2728(98)00058-9
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发表时间：
1998-06-10
影响因子：
4.3
通讯作者：
Brzezinski, P
中科院分区：
文献类型：
--
作者：
Karpefors, M;Ädelroth, P;Brzezinski, P
本文讨论的细胞色素c和泛醇氧化酶是膜结合氧化还原驱动的质子泵，它们将电子电流偶联到穿过膜的质子电流。这种耦合需要控制热力学和/或内部电子和质子转移反应的速率（称为“门控”）。因此，为了理解这些质子泵的结构-功能关系，必须研究单个的电子和质子转移反应。我们通过使用位点定向诱变和光谱技术的结合进行了这样的研究。结果表明，血红素a(3)还原/氧化后的质子摄取/释放通过k途径（包括Thr（I-359）和Lys(I-362)）在ms时间尺度上进行，而不通过d途径（包括Asp（I-132）和Glu(I-286)）。在还原酶与O-2反应过程中，底物和泵送质子均通过d途径（而非k途径）被吸收，时间常数分别为100 μ s和1 ms。因此，必须修改d途径（仅用于泵送质子）的原始角色分配。质子摄取到酶表面的动态研究表明，在质子输入侧，酶表面携带一个由羧酸盐和组氨酸残基组成的质子收集天线，使酶能够以与酶周转率相容的速率拾取质子。这些结果与细胞色素c氧化酶的三维结构一致，表明d途径（而不是k途径）的入口点被处于负静电电位的组氨酸残基网络所包围。(C) 1998爱思唯尔科学有限公司
The cytochrome c and ubiquinol oxidases discussed in this article are membrane-bound redox-driven proton pumps which couple an electron current to a proton current across the membrane. This coupling requires a control of the thermodynamics and/or rates of internal electron- and proton-transfer reactions (termed 'gating'). Therefore, to understand the structure-function relation of these proton pumps, individual electron- and proton-transfer reactions must be investigated. We have undertaken such studies by using a combination of site-directed mutagenesis and spectroscopic techniques. The results show that proton uptake/release upon reduction/oxidation of heme a(3) takes place on a ms-time scale through the K-pathway (including Thr(I-359) and Lys(I-362)), but not through the D-pathway (including Asp(I-132) and Glu(I-286)). During reaction of the reduced enzyme with O-2, both substrate and pumped protons are taken up through the D-pathway (but not through the K-pathway) in a biphasic process with time constants of 100 mu s and 1 ms. Thus, the original assignment of the role of the D-pathway (used only for pumped protons) must be revised. Dynamic studies of proton uptake to the enzyme surface show that on the proton-input side, the surface carries a proton-collecting antenna made of carboxylate and histidine residues which enable the enzyme to pick up protons with a rate compatible to the enzyme turnover rate. These results are consistent with the three-dimensional cytochrome c oxidase structure which shows that the entry point to the D-pathway (but not to the K-pathway) is surrounded by a network of histidine residues within a negative electrostatic potential. (C) 1998 Elsevier Science B.V.