ELECTRON AND PROTON TRANSFER IN REACTION CENTERS

本文讨论了控制电子和质子转移Δ G的因素， 细菌光合反应中心（RC）的研究。 re是 膜内电子转移蛋白的最佳特征 通过耦合电子在细胞中储存化学渗透能， 质子转移 实验和理论的结合 方法将被用来了解如何相互作用的辅因子 和蛋白质指定了辅因子亲和力的相关性质， 结合位点，在AM电化学，和周围残基的pKa。 经典的静电计算将用于分析 不同氧化还原辅因子的电化学中点（E-m's） RC。 将计算RC活动侧和非活动侧的E-m， 确定电子转移是否会受到Δ G差异的限制。 闪光引发的电子转移的光学测量将放置 对来自仲醌的电荷重组速率的限制 沿着蛋白质的非活性侧。 醌的修饰和 结合位点将决定该反应是否受到局部效应的限制 或由中间蛋白质所决定。 对于RC中的两个醌结合位点， 用静电学方法得到的控制E-m的因素图 计算将与醌的详细计算进行比较， 半醌亲和性的网站。 该分析将补充A 丰富的结合常数和Em数据库。 的功能 具有不同电荷分布的醌将被表征 实验和理论上。 玻尔兹曼分布 用蒙特卡罗方法得到了RC中不同的质子化态 对不同电离状态的静电能进行采样， 测定残留pKas。不同氧化还原状态下的pKa位移将显示 质子吸收的途径与电子转移有关。 的 极性质子对计算的pKa和E-m的扰动 将探索与电子转移耦合的运动。 这将是 补充的温度依赖性的实验测量 （BChl）2+BPh-和（BChl）2+QA-之间的Δ G，以研究 在ns上产生（BChl）2+BPh-的显著弛豫的过程 到μ s的时间尺度可以被冻结和表征。

The factors controlling delta Gs of electron and proton transfers in the bacterial photosynthetic reaction center (RC) will be studied. The RC is the best characterized of the intramembrane election transfer proteins that store chemiosmotic energy in the cell by coupling electron and proton transfers. A combination of experimental and theoretical approaches will be used to understand how interactions between cofactors and protein specify the related properties of cofactor affinity for a binding site, in AM electrochemistry, and pKa's of surrounding residues. Classical electrostatics calculations will be used to analyze electrochemical midpoints (E-m's) of the different redox cofactors in RCs. E-m's of active and inactive sides of the RC will be calculated to determine if electron transfer could be limited by delta G differences. Optical measurement of flash initiated electron transfer will place limits on the rate of charge recombination from the secondary quinone along the inactive side of the protein. Modification of the quinone and binding site will determine if this reaction is limited by local effects or by the intervening protein. For the two quinone binding sites in RCs, the picture of factors controlling E-m's obtained by electrostatics calculations will be compared with detailed calculations of quinone and semiquinone affinities for the site. This analysis will complement a rich data base of measured binding constants and Em's. The function of quinones with different charge distributions will be characterized experimentally and theoretically. The Boltzmann distribution of different protonation states in RCs will be obtained by Monte Carlo sampling of the electrostatic energies of different ionization states to determine residue pKas. pKa shifts in different redox states will show the pathway of proton uptake that is coupled to electron transfer. The perturbation of calculated pKa's and E-m's because of polar proton motions coupled to electron transfer will be explored. This will be complemented by experimental measurement of the temperature dependence of the delta G between (BChl)2+BPh- and (BChl)2+QA- to investigate if the processes that yield the substantial relaxation of (BChl)2+BPh- on the ns to mu s time scale can be frozen out and characterized.