The structure of the oxidized state of cytochrome c oxidase - experiments and theory compared.,Journal of Inorganic Biochemistry

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The structure of the oxidized state of cytochrome c oxidase - experiments and theory compared.
Journal of Inorganic Biochemistry ( IF 3.8 ) Pub Date : 2020-02-08 , DOI: 10.1016/j.jinorgbio.2020.111020
Margareta R A Blomberg ₁

Affiliation

Cytochrome c oxidase (CcO), the terminal enzyme in the respiratory chain, reduces molecular oxygen to water. Experimental data on the midpoint potentials of the heme iron/copper active site cofactors do not match the overall reaction energetics, and are also in conflict with the observed efficiency of energy conservation in CcO. Therefore it has been postulated that the ferric/cupric intermediate (the oxidized state) exists in two forms. One form, labelled OH, is presumably involved during catalytic turnover, and should have a high CuB midpoint potential due to a metastable high energy structure. When no more electrons are supplied, the OH state supposedly relaxes to the resting form, labelled O, with a lower energy and a lower midpoint potential. It has been suggested that there is a pure geometrical difference between the OH and O states, obtained by moving a water molecule inside the active site. It is shown here that the difference between the two forms of the oxidized state must be of a more chemical nature. The reason is that all types of geometrically relaxed structures of the oxidized intermediate have similar energies, all with a high proton coupled reduction potential in accordance with the postulated OH state. One hypothesized chemical modification of the OH state is the transfer of an extra proton, possibly internal, into the active site. Such a protonated state has several properties that agree with experimental data on the relaxed oxidized state, including a decreased midpoint potential.

中文翻译：

细胞色素C氧化酶氧化态的结构-实验与理论比较。

细胞色素c氧化酶（CcO）是呼吸链中的末端酶，可将分子氧还原为水。关于血红素铁/铜活性位点辅助因子中点电位的实验数据与总体反应能不匹配，并且也与在CcO中观察到的节能效率相矛盾。因此，假定铁/铜中间体（氧化态）以两种形式存在。一种标记为OH的形式可能在催化转换过程中涉及，由于亚稳态的高能结构，它应具有较高的CuB中点电势。如果不再提供电子，则OH态会以较低的能量和较低的中点电势松弛为标记为O的静止形式。有人建议在OH和O状态之间存在纯几何差异，通过在活动位点内移动水分子获得。在此表明，两种形式的氧化态之间的差异必须具有更大的化学性质。原因是氧化中间体的所有类型的几何弛豫结构都具有相似的能量，所有能量均根据假定的OH状态具有高质子耦合的还原电势。一种假设的OH状态化学修饰是可能在内部的额外质子转移到活性位点。这样的质子化状态具有与关于松弛的氧化态的实验数据一致的若干性质，包括降低的中点电势。原因是氧化中间体的所有类型的几何弛豫结构都具有相似的能量，所有能量均根据假定的OH状态具有高质子耦合的还原电势。一种假设的OH状态化学修饰是可能在内部的额外质子转移到活性位点。这样的质子化状态具有与关于松弛的氧化态的实验数据一致的若干性质，包括降低的中点电势。原因是氧化中间体的所有类型的几何弛豫结构都具有相似的能量，所有能量均根据假定的OH状态具有高质子耦合的还原电势。一种假设的OH状态化学修饰是可能在内部的额外质子转移到活性位点。这样的质子化态具有与松弛氧化态的实验数据相符的若干性质，包括降低的中点电势。

更新日期：2020-02-10

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