Energetics for oxidation of a bound manganese cofactor in modified bacterial reaction centers.
Energetics for oxidation of a bound manganese cofactor in modified bacterial reaction centers.
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在改良的细菌反应中心中氧化结合的锰辅助因子的能量学。
作者：
L. Kálmán;L. Kálmán;Joann C. Williams;James P. Allen
的能量的Mn辅因子绑定到改性的反应中心进行了测定，包括氧化/还原中点电位和电子转移的自由能差。为了确定这些性质，设计了一系列具有在pH 9.0下以1 μM的解离常数结合Mn 2+的金属离子结合位点的球形红细菌突变体（Thielges等人（2005）Biochemistry 44，7389-7394）。除了锰结合位点，每个突变体附近的细菌叶绿素二聚体，P，这导致改变P/P+氧化/还原中点电位，其范围从480 mV到800 mV以上的野生型相比，505 mV的变化。结合的Mn 2+是氧化还原活性的，并且在光激发后可以快速还原氧化的初级电子供体P+。P+减少的程度被发现系统范围从一个完整的减少在突变体与高P/P+中点电位的突变体没有减少与野生型的潜力相当。Mn 2+氧化程度对P/P+中点电位的这种依赖性可以使用平衡模型和能斯特方程来理解，在pH 9下产生625 mV的Mn 2 +/Mn 3+氧化/还原中点电位。在碳酸氢盐的存在下，发现Mn 2 +/Mn 3+电位低90 mV，值为535 mV，表明碳酸氢盐用作结合Mn的配体。在不存在碳酸氢盐的情况下，当P/P+中点电位从670 mV增加到约805 mV时，电子转移速率的测量得到Mn 2+氧化的速率常数范围为30至120 s（-1）。在碳酸氢盐的存在下，每个突变体的速率增加，值范围为65至165 s（-1），反映了由于较低的Mn 2 +/Mn 3+中点电位导致的自由能差增加。速率常数对P/P+中点电位的这种依赖性可以使用Marcus关系来理解，该关系产生的最大速率常数和重组能量的极限分别为至少150 s（-1）和290 meV。这些结果的影响进行了讨论，在能量的蛋白质与氧化还原活性锰辅因子，特别是Mn 4Ca辅因子的光系统II。
The energetics of a Mn cofactor bound to modified reaction centers were determined, including the oxidation/reduction midpoint potential and free energy differences for electron transfer. To determine these properties, a series of mutants of Rhodobacter sphaeroides were designed that have a metal-ion binding site that binds Mn2+ with a dissociation constant of 1 μM at pH 9.0 (Thielges et al. (2005) Biochemistry 44, 7389-7394). In addition to the Mn binding site, each mutant had changes near the bacteriochlorophyll dimer, P, that resulted in altered P/P+ oxidation/reduction midpoint potentials, which ranged from 480 mV to above 800 mV compared to 505 mV for wild type. The bound Mn2+ is redox active and after light excitation can rapidly reduce the oxidized primary electron donor, P+. The extent of P+ reduction was found to systematically range from a full reduction in the mutants with high P/P+ midpoint potentials to no reduction in the mutant with a potential comparable to wild type. This dependence of the extent of Mn2+ oxidation on the P/P+ midpoint potential can be understood using an equilibrium model and the Nernst equation, yielding a Mn2+/Mn3+ oxidation/reduction midpoint potential of 625 mV at pH 9. In the presence of bicarbonate, the Mn2+/Mn3+ potential was found to be 90 mV lower with a value of 535 mV suggesting that the bicarbonate serves as a ligand to the bound Mn. Measurement of the electron transfer rates yielded rate constants for Mn2+ oxidation ranging from 30 to 120 s(-1) as the P/P+ midpoint potentials increased from 670 mV to approximately 805 mV in the absence of bicarbonate. In the presence of bicarbonate, the rates increased for each mutant with values ranging from 65 to 165 s(-1), reflecting an increase in the free energy difference due to the lower Mn2+/Mn3+ midpoint potential. This dependence of the rate constant on the P/P+ midpoint potential can be understood using a Marcus relationship that yielded limits of at least 150 s(-1) and 290 meV for the maximal rate constant and reorganization energy, respectively. The implications of these results are discussed in terms of the energetics of proteins with redox active Mn cofactors, in particular, the Mn4Ca cofactor of photosystem II.
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DOI：
10.1016/s0005-2728(00)00069-4
发表时间：
2000-05
期刊：
Biochimica et biophysica acta
影响因子：
--
作者：
Cecilia Tommos;Gerald T. Babcock
通讯作者：
Cecilia Tommos;Gerald T. Babcock
影响因子：
2.9
作者：
Lévêque, VJP;Vance, CK;Silverman, DN
通讯作者：
Silverman, DN
球形红细菌反应中心电子转移反应的动力学和自由能隙。
影响因子：
2.9
作者：
Nagarajan,V;Parson,WW;Davis,D;Schenck,CC
通讯作者：
Schenck,CC
影响因子：
15
作者：
Gunderson, William A.;Zatsman, Anna I.;Emerson, Joseph P.;Farquhar, Erik R.;Que, Lawrence, Jr.;Lipscomb, John D.;Hendrich, Michael P.
通讯作者：
Hendrich, Michael P.
化学在结构-功能链接中的至关重要性：操纵含铁超氧化物歧化酶中的氢键。
影响因子：
2.9
作者：
Yikilmaz,Emine;Rodgers,DavidW;Miller,Anne-Frances
通讯作者：
Miller,Anne-Frances