On the rate distribution analysis of kinetic data using the maximum entropy method: Applications to myoglobin relaxation on the nanosecond and femtosecond timescales
On the rate distribution analysis of kinetic data using the maximum entropy method: Applications to myoglobin relaxation on the nanosecond and femtosecond timescales
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DOI：
10.1021/jp0101209
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发表时间：
2001-08-16
影响因子：
3.3
通讯作者：
Champion, PM
中科院分区：
文献类型：
--
作者：
Kumar, ATN;Zhu, LY;Champion, PM
我们讨论了最大熵方法（MEM）的应用，从动力学实验中的纳秒到飞秒的时间尺度上的速率分布的提取。我们首先提出了模拟数据截断（典型的纳秒实验）的影响恢复MEM的速率分布。拉伸指数衰减被认为是一个例子来证明，如果真实的底层过程的速率分布包括更快的时间尺度比包含在实验数据集内，MEM可以引入不必要的功能，扩展到速度空间的较慢的区域。这一观察结果与MEM的应用有关，以从涉及蛋白质等复杂分子的松弛的动力学实验中获得速率分布，其中分布中的特征有时被解释为蛋白质构象substates的静态分布。作为一个实验的例子，我们提出了一个MEM分析的温度依赖性的双生再结合动力学的碳单氧肌红蛋白在室温附近，并找到一个势垒高度为18 kJ/mol。我们还考虑应用MEM超快泵浦探测瞬态吸收数据，其中需要考虑到的动力学和有限的脉冲自相关宽度，有效地卷积到所观察到的材料响应的非单调性的可能性。作为例子，在可见光区的几个波长监测的Mb和MbNO的飞秒激光物理学的MEM分析。
We discuss the application of the maximum entropy method (MEM) to the extraction of rate distributions from kinetics experiments on the nanosecond to femtosecond time scale. We first present simulations to show the effects of data truncation (typical of nanosecond experiments) on rate distributions recovered by MEM. The stretched exponential decay is considered as an example to demonstrate that if the true distribution of rates for the underlying process includes faster time scales than are contained within the experimental data set, MEM can introduce unwarranted features that extend into the slower regions of rate space. This observation has relevance to the application of MEM to obtain rate distributions from kinetic experiments involving the relaxation of complex molecules like proteins, where features in the distribution are sometimes interpreted as static distributions of protein conformational substates. As an experimental example, we present an MEM analysis of the temperature dependence of the geminate rebinding kinetics of carbonmonoxy myoglobin near room temperature and find a barrier height of 18 kJ/mol. We also consider the application of MEM to ultrafast pump-probe transient absorption data, where one needs to take into account the possibility of nonmonotonicity in the kinetics and the finite pulse autocorrelation width that effectively convolves into the observed material responses. The MEM analyses of the femtosecond photophysics of Mb and MbNO, monitored at several wavelengths in the visible region, are presented as examples.