Data from earlier studies showed that minor structural changes at the surface of cytochrome c oxidase, in one of the proton-input pathways (the D pathway), result in dramatically decreased activity and a lower proton-pumping stoichiometry. To further investigate how changes around the D pathway orifice influence functionality of the enzyme, here we modified the nearby C-terminal loop of subunit I of the Rhodobacter sphaeroides cytochrome c oxidase. Removal of 16 residues from this flexible surface loop resulted in a decrease in the proton-pumping stoichiometry to <50% of that of the wild-type enzyme. Replacement of the protonatable residue Glu552, part of the same loop, by an Ala, resulted in a similar decrease in the proton-pumping stoichiometry without loss of the O2-reduction activity or changes in the proton-uptake kinetics. The data show that minor structural changes at the orifice of the D pathway, at a distance of ~40 Å from the proton gate of cytochrome c oxidase, may alter the proton-pumping stoichiometry of the enzyme.

中文翻译：

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细胞色素C氧化酶表面的结构变化会改变质子泵的化学计量。

早期研究的数据表明，在质子输入途径（D途径）之一中，细胞色素C氧化酶表面的微小结构变化导致活性显着降低，质子泵浦化学计量降低。为了进一步研究D通路孔周围的变化如何影响该酶的功能，在这里我们修饰了球形球形红细菌细胞色素C氧化酶I亚基的C末端环。从该柔性表面环中除去16个残基会导致质子泵送化学计量比降低至野生型酶的50％。用Ala代替同一环中一部分的可质子化残基Glu552，在不损失O2还原活性或质子吸收动力学变化的情况下，导致质子泵化学计量的相似降低。