Effect of Protein Conformation Fluctuation on the Election Transfer Rate through Protein Media

通过蛋白质介质的电子转移通常是一种远程电子转移，即通过隧道机制，从蛋白质环境感受到电子气氛，从供体到受体的电子转移。到目前为止，人们认为将会有一个区域，电子可能会通过该区域转移。通常，化学键等被认为是它的候选。如果发生这种情况，电子隧穿基元不会因为蛋白质构象的热涨落而显著改变，因为蛋白质中的化学键不会因为蛋白质构象的涨落而改变。然而，根据我们通过分子动力学(MID)模拟实现蛋白质构象涨落和用量子化学理论计算电子隧穿矩阵元的研究结果，蛋白质的构象涨落会使电子隧穿矩阵元素发生快速而巨大的变化。作为其机制，人们认为…越多的隧穿电流相间干扰作用越显著。事实上，这是一个非常有趣的问题，电子隧穿矩阵元中的值的快速波动如何影响ET率。我们构造了一个新的非康登理论，在该理论中，我们可以利用经典分子动力学模拟得到的电子隧道矩阵元的时间关联函数。在该理论中，对核运动进行了量子修正，从而满足了正反向速率的详细平衡条件。通过用这一新理论分析蛋白质介质中的电子转移，我们发现电子隧穿矩阵元的快速起伏对电子传输速率的能隙依赖性有很大的影响。也就是说，我们发现在远正区和远反区存在非弹性隧穿机制，两个区的ET率都有很大的提高。我们调查了支持这一预测的实验数据。然后，我们发现，在Rehm-Weller荧光猝灭实验中，在很大的能隙范围内，ET率没有明显的衰减，这与我们的理论是一致的：

Electron transfer (ET) through protein media is, in general, a long-range ET Namely, ETs take place from donor to acceptor by the tunneling mechanism, by feeling electric atmosphere from protein environment. So far, it was considered that there will be a region through which an electron is likely to be transferred. Usually chemical bonds and so on are considered as its candidate. If it happens, the election tunneling matrix element will not be changed considerably by the thermal fluctuation of protein conformation, because chemical bonds in the protein are not changed by the conformation fluctuation of protein. However, according to the results of our study in which protein conformation fluctuations are realized by the molecular dynamics (MID) simulation and electron tunneling matrix elements are calculated by the quantum chemical theory, electron tunneling matrix element is changed rapidly and greatly by the conformation fluctuation of proteins. As its mechanism, it is considered that … More interference among phases of tunneling currents works significantly. Indeed, it is a very interesting problem how the rapid fluctuation of the value in the electron tunneling matrix element affects the ET rate. We constructed a new non-Condon theory in which we can use the time correlation function of the electron tunneling matrix element obtained by the classical MD simulation. In this theory, the quantum, correction to the nuclear motion is performed and so, the detailed balance condition for the forward and backward rates is satisfied. As a result of analyzing the electron transfer in protein media using this new theory, we found that the energy gap dependence of the ET rate is greatly affected by the rapid fluctuation of the electron tunneling matrix element. Namely; we found that an inelastic tunneling mechanism works at the far normal region and far inverted region and then, the ET rates are much enhanced in both regions. We surveyed the experimental data which support this prediction. Then, we found that the ET rate does not decay appreciably at the very large energy gap in the Rehm-Weller experiment for the fluorescence quenching in polar solution, which is consistent with our theory: Less