Kinetic performance and energy profile in a roller coaster electron transfer chain:: A study of modified tetraheme-reaction center constructs
Kinetic performance and energy profile in a roller coaster electron transfer chain:: A study of modified tetraheme-reaction center constructs
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DOI：
10.1021/ja058131t
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发表时间：
2006-03-29
影响因子：
15
通讯作者：
Nagashima, KVP
中科院分区：
文献类型：
--
作者：
Alric, J;Lavergne, J;Nagashima, KVP
在许多电子传递蛋白质中，辅因子的排列意味着一系列的上坡和下坡步骤。这种安排的动力学影响进行检查，在本工作中，嵌合光合反应中心的研究的基础上，通过表达的四血红素亚基从芽绿球藻在另一个紫色细菌，Rubrivivax gelatinosus。血红素c（559）是主要供体P的直接电子供体，血红素c（559）环境的定点突变诱导了血红素中点电位在400 mV范围内的改变。这导致了相邻载体的表观中点电位的变化，从而估计了氧化还原中心之间的相互作用。在探索范围的两端，电子转移链的能量分布呈现出额外的上坡台阶，无论是下游或上游的c（559）。这些修改引起了显着的变化的电子转移速率跨四血红素亚基，这变得类似于100倍慢的突变体中的中点电位的C-559是最低的。动力学的理论分析，预测位移的限速步骤时，降低c559的电位。一个合理的协议与数据相结合时，得到这种治疗与电子转移理论预测的速率为个人的速率常数。
In many electron-transfer proteins, the arrangement of cofactors implies a succession of uphill and downhill steps. The kinetic implications of such arrangements are examined in the present work, based on a study of chimeric photosynthetic reaction centers obtained by expressing the tetraheme subunit from Blastochloris viridis in another purple bacterium, Rubrivivax gelatinosus. Site-directed mutations of the environment of heme c(559), which is the immediate electron donor to the primary donor P, induced modifications of this heme's midpoint potential over a range of 400 mV. This resulted in shifts of the apparent midpoint potentials of the neighboring carriers, yielding estimates of the interactions between redox centers. At both extremities of the explored range, the energy profile of the electron-transfer chain presented an additional uphill step, either downstream or upstream from c(559). These modifications caused conspicuous changes of the electron-transfer rate across the tetraheme subunit, which became similar to 100-fold slower in the mutants where the midpoint potential of C-559 was lowest. A theoretical analysis of the kinetics is presented, predicting a displacement of the rate-limiting step when lowering the potential of c559. A reasonable agreement with the data was obtained when combining this treatment with the rates predicted by electron transfer theory for the individual rate constants.