Zhou Jian-Min, Gold Nicholas D, Martin Vincent J J, Wollenweber Eckhard, Ibrahim Ragai K
Plant Biochemistry Laboratory, Concordia University, Montréal, Quebec, Canada H4B 1R6.
Biochim Biophys Acta. 2006 Jul;1760(7):1115-24. doi: 10.1016/j.bbagen.2006.02.008. Epub 2006 Mar 10.
Flavonoid compounds are ubiquitous in nature. They constitute an important part of the human diet and act as active principles of many medicinal plants. Their O-methylation increases their lipophilicity and hence, their compartmentation and functional diversity. We have isolated and characterized a full-length flavonoid O-methyltransferase cDNA (TaOMT2) from a wheat leaf cDNA library. The recombinant TaOMT2 protein was purified to near homogeneity and tested for its substrate preference against a number of phenolic compounds. Enzyme assays and kinetic analyses indicate that TaOMT2 exhibits a pronounced preference for the flavone, tricetin and gives rise to three methylated enzyme reaction products that were identified by TLC, HPLC and ESI-MS/MS as its mono-, di- and trimethyl ether derivatives. The sequential order of tricetin methylation by TaOMT2 is envisaged to proceed via its 3'-mono--->3',5'-di--->3',4',5'-trimethyl ether derivatives. To our knowledge, this is the first report of a gene product that catalyzes three sequential O-methylations of a flavonoid substrate.
黄酮类化合物在自然界中广泛存在。它们是人类饮食的重要组成部分，也是许多药用植物的活性成分。它们的O - 甲基化增加了其亲脂性，从而增加了它们的区室化作用和功能多样性。我们从小麦叶片cDNA文库中分离并鉴定了一个全长黄酮类O - 甲基转移酶cDNA（TaOMT2）。重组TaOMT2蛋白被纯化至接近均一，并针对多种酚类化合物测试了其底物偏好性。酶活性测定和动力学分析表明，TaOMT2对黄酮类化合物三羟黄酮表现出明显的偏好，并产生三种甲基化酶反应产物，通过薄层色谱（TLC）、高效液相色谱（HPLC）和电喷雾串联质谱（ESI - MS/MS）鉴定为其一甲基、二甲基和三甲基醚衍生物。TaOMT2对三羟黄酮进行甲基化的顺序被设想为通过其3'-单甲基醚衍生物→3',5'-二甲基醚衍生物→3',4',5'-三甲基醚衍生物的过程。据我们所知，这是关于催化黄酮类底物进行三个连续O - 甲基化的基因产物的首次报道。
