Bathelt Christine M, Mulholland Adrian J, Harvey Jeremy N
Centre for Computational Chemistry, School of Chemistry, University of Bristol, Cantocks' Close, Bristol BS8 1TS, UK.
J Phys Chem A. 2008 Dec 18;112(50):13149-56. doi: 10.1021/jp8016908.
The mechanism of benzene hydroxylation was investigated in the realistic enzyme environment of the human CYP 2C9 by using quantum mechanical/molecular mechanical (QM/MM) calculations of the whole reaction profile using the B3LYP method to describe the QM region. The calculated QM/MM barriers for addition of the active species Compound I to benzene are consistent with experimental rate constants for benzene metabolism in CYP 2E1. In contrast to gas-phase model calculations, our results suggest that competing side-on and face-on geometries of arene addition may both occur in the case of aromatic ring oxidation in cytochrome P450s. QM/MM profiles for three different rearrangement pathways of the initially formed sigma-adduct, leading to formation of epoxide, ketone, and an N-protonated porphyrin species, were calculated. Our results suggest that epoxide and ketone products form with comparable ease in the face-on pathway, whereas epoxide formation is preferred in the side-on pathway. Additionally, rearrangement to the N-protonated porphyrin species was found to be competitive with side-on epoxide formation. This suggests that overall, the competition between formation of epoxide and phenol final products in P450 oxidation of aromatic substrates is quite finely balanced.
通过使用量子力学/分子力学（QM/MM）方法对整个反应过程进行计算，采用B3LYP方法描述QM区域，在人CYP 2C9的实际酶环境中研究了苯羟基化的机制。计算得到的活性物种化合物I与苯加成的QM/MM势垒与CYP 2E1中苯代谢的实验速率常数一致。与气相模型计算不同，我们的结果表明，在细胞色素P450s中芳香环氧化的情况下，芳烃加成的竞争侧基和正面几何构型可能都会出现。计算了最初形成的σ-加合物的三种不同重排途径的QM/MM剖面图，这些途径导致环氧化物、酮和N-质子化卟啉物种的形成。我们的结果表明，在正面途径中环氧化物和酮产物的形成难易程度相当，而在侧基途径中环氧化物的形成更为有利。此外，发现重排为N-质子化卟啉物种与侧基环氧化物的形成存在竞争。这表明总体而言，在P450氧化芳香底物过程中环氧化物和苯酚最终产物形成之间的竞争相当微妙。
