Cytochrome c oxidase exhibits a rapid conformational change upon reduction of CuA: a tryptophan fluorescence study.
Cytochrome c oxidase exhibits a rapid conformational change upon reduction of CuA: a tryptophan fluorescence study.
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细胞色素 c 氧化酶在 CuA 还原时表现出快速构象变化：一项色氨酸荧光研究。
DOI：
10.1021/bi00397a017
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发表时间：
1987
期刊：
影响因子：
2.9
通讯作者：
Chan,SI
中科院分区：
文献类型：
--
作者：
Copeland,RA;Smith,PA;Chan,SI
修订稿收到1987年6月12日摘要：当细胞色素C氧化酶被还原时，它经历了构象变化，其色氨酸荧光最大值从329 nm移动到345 nm。对该酶的配基结合、混合价形式的研究表明，这种构象变化依赖于低电位金属中心细胞色素a和CuA的氧化还原状态。Cs+不能有效地猝灭被氧化的细胞色素c氧化酶的本征荧光，但对还原后的酶有明显的猝灭作用，其Stern-Volmer常数为0.69。这些观察结果，加上发射最大值的显著红移，表明释放的色氨酸残基在还原的酶中变得更容易溶于溶剂。停流光谱表明，这种构象转变是在低电势位被还原后迅速发生的，其假一级速率常数为4.07±0.40 S“1。由色氨酸荧光监测到的构象变化可能与先前提出的细胞色素C氧化酶的”开闭“转变有关。用细胞色素c还原滴定氰化物抑制的酶，表明荧光位移对添加的电子等价物的非线性响应。已经开发出一种理论上处理氰化物抑制酶的两个相互作用部位的还原，它给出了每个氧化还原状态的布居数作为酶接受的电子总数的函数。这种处理取决于两个参数：两种金属之间的氧化还原电位的差异和氧化还原中心之间的氧化还原相互作用。通过使用氰化物抑制酶这两个参数的文献值，在三种情况下评估了预期的行为：(I)由细胞色素a和CUA还原引起的构象变化(双电子过程)，(Ii)由细胞色素a还原引起的构象变化(单电子过程)，以及(Iii)由CUA还原引起的构象变化(也是单电子过程)。这一理论处理的结果有力地表明，当前的数据以及来自其他实验室的独立数据与CUA中心的减少引起的构象变化最一致。讨论了这种构象变化的性质及其在该酶质子泵机制中的应用。嗜酸性生物之所以蓬勃发展，是因为它们利用分子氧来驱动三磷酸腺苷的生物合成(Lehninger，1973)。在这些生物体中，氧气还原为水是由呼吸电子转移链中的末端酶--细胞色素C氧化酶催化的。在哺乳动物中，细胞色素c氧化酶横跨线粒体内膜，接受来自胞质侧的细胞色素c铁的电子，并将它们提供给氧气。在该反应中消耗的标量质子从膜的基质侧被吸收。在电子转移反应中使用了四个金属辅因子，两个血红素铁(细胞色素a和<；Z3)和两个铜离子(CuA和CuB)。细胞色素a和CUA位于酶的电子输入侧，是细胞色素c的主要电子受体。细胞色素A3和CUB共同形成氧结合的双核中心(Wikstrom等人，1981)。除了它们在电子转移中的作用外，这些金属中心中至少有一个与细胞色素c氧化酶中氧化还原连接的质子泵送活动有关，将质子从基质转移到膜的胞液侧以对抗…。
Revised Manuscript Received June 12, 1987 abstract: When cytochrome c oxidase is reduced, it undergoes a conformational change that shifts its tryptophan fluorescence maximum from 329 to 345 nm. Studies of ligand-bound, mixed-valence forms of the enzyme show that this conformational change is dependent on the redox state of the low-potential metal centers, cytochrome a and CuA. The intrinsic fluorescence of oxidized cytochrome c oxidase is not effectively quenched by Cs+; however, marked quenching is observed for the reduced enzyme with a Stern-Volmer constant of 0.69. These observations, together with the significant red shift of the emission maximum, suggest that the emitting tryptophan residues are becoming more solvent accessible in the reduced enzyme. Stopped-flow spectrashow that this conformational transition occurs rapidly upon reduction of the low-potential sites with a pseudo-first-order rate constant of 4.07±0.40 s" 1. The conformational change monitored by tryptophan fluorescence is suggested to be related to the previously proposed “open-closed” transition of cytochrome c oxidase. Reductive titration of the cyanide-inhibited enzyme with ferrocytochrome c shows a nonlinear response of the fluorescence shift to added electron equivalents. A theoretical treatment of the reduction of the two interacting sites of the cyanide-inhibited enzyme has been developed that gives the population of each redox state as a function of the total number of electrons accepted by the enzyme. This treatment depends on two parameters: the difference in redox potential between the two metals and the redox interaction between the redox centers. By use of literature values of these two parameters for the cyanide-inhibited enzyme, the expected behavior has been evaluated for three situations:(i) a conformational change induced by reduction of both cytochrome a and CuA (a two-electron process),(ii) a conformational change induced by reduction of cytochrome a (a one-electron process), and (iii) a conformational change induced by reduction of CuA (also a one-electron process). The results of this theoretical treatment strongly suggest that the current data, as well as independent data from other laboratories, are most consistent with a conformational change induced by reduction of the CuA center. The nature of this conformational change and itsimplication for proton pumping mechanisms of the enzyme are discussed..^^. erobic organisms have flourished because of the efficient means by which they utilize molecular oxygen to drive the biosynthesis of adenosine triphosphate (Lehninger, 1973). The reduction of dioxygen to water is catalyzed in these organisms by the terminal enzyme in the respiratory electron-transfer chain, cytochrome c oxidase. In mammals, cytochrome c oxidase spans the inner mitochondrial membrane, accepting electrons from ferrocytochrome c on the cytosolic side and donating them to dioxygen. The scalar protons consumed in this reaction are taken up from the matrix side of the mem-brane. Four metal cofactors are used in the electron-transfer reaction, two heme irons (cytochromes a and< z3) and two copper ions (CuA and CuB). Cytochrome a and CuA are located on the electron input side of the enzyme and serve as the primary electron acceptors from cytochrome c. Cytochrome a3 and CuB together form the binuclear center for dioxygen binding (Wikstrom et al., 1981). Apart from their role in electron transfer, at least one of these metal centers is associated with a redox-linked proton pumping activity in cytochrome c oxidase, translocating protons from the matrix to the cytosolic side of the membrane against a …
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影响因子：
2.9
作者：
DUNN, MF;PATTISON, SE;QUIEL, E
通讯作者：
QUIEL, E
细胞色素 a 的氧化还原状态及其对蛋白酶的敏感性。
影响因子：
2.7
作者：
T. Yamamoto;K. Okukuki
通讯作者：
K. Okukuki
细胞色素 c 氧化酶中 830 nm 发色团的滴定和稳态行为。
DOI：
10.1042/bj2030541
发表时间：
1982
期刊：
The Biochemical journal
影响因子：
--
作者：
P. Nicholls;G. Chanady
通讯作者：
G. Chanady
影响因子：
2.9
作者：
HILL, BC;HOROWITZ, PM;ROBINSON, NC
通讯作者：
ROBINSON, NC
细胞色素氧化酶内的金属位点协同作用。
DOI：
--
发表时间：
1984
期刊：
The Journal of biological chemistry
影响因子：
--
作者：
Goodman,G
通讯作者：
Goodman,G