摘要
采用密度泛函理论(DFT)对P450酶活性中心铁卟啉Cpd I催化二乙基亚硝胺(NDEA)代谢活化的反应机理进行了研究.结果表明,Cpd I催化NDEA羟基化的过程包含氢抽提反应和回弹反应2个步骤.其中,氢抽提反应为控速步骤,氢自由基从NDEA转移到铁卟啉的Fe O上,是典型的氢原子传递(HAT)过程;紧接着铁卟啉上的羟基经历无能垒的反应过程回弹到NDEA自由基上,形成羟基化代谢产物.NDEA羟基化过程中高自旋态(HS)和低自旋态(LS)均参与反应,整个羟基化过程呈现明显的双态反应性(TSR).研究比较了NDEA分子侧链上Cα—H和Cβ—H羟基化反应的差异,得到Cα—H和Cβ—H羟基化所需跨越的能垒分别为57.7/57.7 k J/mol(LS/HS)和76.4/74.3 k J/mol(LS/HS),表明Cα—H比Cβ—H更易于在P450作用下发生羟基化;此外,Cβ—H羟基化所需克服的能垒并未过高,使得Cβ—H羟基化在生理条件下完全也有可能发生.本研究为深入揭示亚硝胺经代谢活化导致癌症的作用机制提供了可靠的理论依据.
N-Nitrosamines(NAs)are an important family of carcinogens widely existing in the environment.NAs are metabolic activated by cytochrome P450 in vivo and generate hydroxylated products,which further decompose to active electrophiles to alkylated DNA bases,leading to the occurrence of cancer.Therefore,P450-catalyzed metabolic activation is a pivotal step in the carcinogenesis of NAs.In this study,the metabolic mechanism of N-nitrosodiethylamine(NDEA)catalyzed by the active center of P450,ferric porphyrin,was investigated using density functional theory(DFT)computations.The results indicated that the hydroxylation of NDEA catalyzed by ferric porphyrin included two steps,hydrogen abstraction and rebound reaction.Hydrogen abstraction is the rate-limiting step and is a typical hydrogen atom transfer(HAT)procedure,in which a hydrogen free radical transfers from NDEA to the Fe O group of ferric porphyrin.Subsequently,the hydroxyl group on porphyrin rebounds to the NDEA radical via a barrierless process,resulting in the formation of hydroxylation product.High-and low-spin states of ferric porphyrin equally participate the hydroxylation of NDEA,which exhibits obvious characters of two-state reactivity(TSR).The hydroxylation mechanisms of C^αH and C^βH in the side chain of NDEA was compared.The energy barriers of the hydroxylation of C^αH and C^βH are 57.7/57.7 k J/mol(LS/HS)and 76.4/74.3 k J/mol(LS/HS),respectively.This suggests that the hydroxylation of C^αH is more favorable than C^βH.In addition,the hydroxylation of C^βH is also possible to occur under physiological conditions because of the somewhat low energy barrier.This research provides plausible explanation for the mechanism of metabolic activation and carcinogenesis of N-nitrosamines.
作者
杨顺莉
赵丽娇
范腾蛟
任婷
钟儒刚
YANG Shun-li;ZHAO Li-jiao;FAN Teng-jiao;REN Ting;ZHONG Ru-gang(Beijing Key Laboratory of Environmental&Viral Oncology,College of Life Science and Bioengineering,Beijing University of Technology,Beijing 100124,China)
出处
《分子科学学报》
CAS
CSCD
北大核心
2017年第1期15-23,共9页
Journal of Molecular Science
基金
国家自然科学基金资助项目(21277001)
北京市自然科学基金资助项目(7162015)
北京市教委科技资助项目(PXM2015_014204_500175)
