Department of Plant and Soil Sciences, University of Kentucky, Lexington, Kentucky 40546-0312, USA.
J Agric Food Chem. 2012 Nov 21;60(46):11586-91. doi: 10.1021/jf303681u. Epub 2012 Nov 12.
Nornicotine is the demethylation product of nicotine and the precursor of tobacco-specific nitrosamine N'-nitrosonornicotine (NNN) in tobacco (Nicotiana tabacum L.). There is an inconsistent enantiomer fraction (EF) of nornicotine reported in the literature. The objective of this study was to explore possible mechanisms to account for the variable EF(nnic) in tobacco. A survey of tobacco with different demethylating capabilities confirmed that there was variable EF(nnic). Experiments of induction and inhibition of the major nicotine demethylase CYP82E4 activity in tobacco demonstrated that CYP82E4 selectively demethylated (S)-nicotine and resulted in different EF(nnic) in tobacco leaves. Results from plants with silenced demethylases by RNAi suggested that other demethylases selectively used (R)-nicotine and resulted in high EF(nnic). In summary, enantioselective demethylation likely plays an important role in contributing to a large and variable EF(nnic) observed in tobacco.
去甲烟碱是尼古丁的脱甲基产物，也是烟草特有亚硝胺 N'-亚硝基降烟碱（NNN）的前体。文献中报道的去甲烟碱对映体分数（EF）不一致。本研究旨在探讨可能的机制来解释烟草中去甲烟碱 EF(nnic)的变化。对具有不同脱甲基能力的烟草进行调查证实，EF(nnic)存在可变性。烟草中主要尼古丁脱甲基酶 CYP82E4 活性的诱导和抑制实验表明，CYP82E4 选择性地脱甲基化（S）-尼古丁，导致烟草叶片中不同的 EF(nnic)。通过 RNAi 沉默脱甲基酶的植物实验表明，其他脱甲基酶选择性地使用（R）-尼古丁，导致高 EF(nnic)。总之，对映体选择性脱甲基可能在导致烟草中观察到的大而可变的 EF(nnic)中发挥重要作用。
