The Biodesign Institute at Arizona State University, Arizona State University, Tempe, Arizona 85287-5201, USA.
J Phys Chem B. 2011 Sep 29;115(38):11230-8. doi: 10.1021/jp204239v. Epub 2011 Aug 25.
The process of electron transfer from the special pair, P, to the primary electron donor, H(A), in quinone-depleted reaction centers (RCs) of Chloroflexus (Cf.) aurantiacus has been investigated over the temperature range from 10 to 295 K using time-resolved pump-probe spectroscopic techniques. The kinetics of the electron transfer reaction, P* → P(+)H(A)(-), was found to be nonexponential, and the degree of nonexponentiality increased strongly as temperature decreased. The temperature-dependent behavior of electron transfer in Cf. aurantiacus RCs was compared with that of the purple bacterium Rhodobacter (Rb.) sphaeroides . Distinct transitions were found in the temperature-dependent kinetics of both Cf. aurantiacus and Rb. sphaeroides RCs, at around 220 and 160 K, respectively. Structural differences between these two RCs, which may be associated with those differences, are discussed. It is suggested that weaker protein-cofactor hydrogen bonding, stronger electrostatic interactions at the protein surface, and larger solvent interactions likely contribute to the higher transition temperature in Cf. aurantiacus RCs temperature-dependent kinetics compared with that of Rb. sphaeroides RCs. The reaction-diffusion model provides an accurate description for the room-temperature electron transfer kinetics in Cf. aurantiacus RCs with no free parameters, using coupling and reorganization energy values previously determined for Rb. sphaeroides , along with an experimental measure of protein conformational diffusion dynamics and an experimental literature value of the free energy gap between P* and P(+)H(A)(-).
已使用时间分辨泵浦探针光谱技术在 10 至 295 K 的温度范围内研究了从特殊对 P 到醌耗尽的反应中心 (RC) 中的初级电子供体 H(A) 的电子转移过程，来自 Chloroflexus (Cf.) aurantiacus。电子转移反应 P*→P(+)H(A)(-)的动力学是非指数的，并且随着温度的降低，非指数性的程度强烈增加。比较了 Cf. aurantiacus RC 中与紫色细菌 Rhodobacter (Rb.) sphaeroides 的温度依赖性电子转移行为。在 Cf. aurantiacus 和 Rb. sphaeroides RC 的温度依赖性动力学中均发现了明显的转变，分别在 220 和 160 K 左右。讨论了这两个 RC 之间的结构差异，这些差异可能与这些差异有关。有人建议，较弱的蛋白质辅因子氢键，较强的蛋白质表面静电相互作用以及较大的溶剂相互作用可能导致 Cf. aurantiacus RC 的温度依赖性动力学中的转变温度高于 Rb. sphaeroides RC。反应扩散模型使用先前为 Rb. sphaeroides 确定的耦合和重组能值，以及蛋白质构象扩散动力学的实验测量值和 P*与 P(+)H(A)(-)之间的自由能间隙的实验文献值，为 Cf. aurantiacus RC 的室温电子转移动力学提供了准确的描述，而无需自由参数。
