The methionine chain elongation pathway in the biosynthesis of glucosinolates in Eruca sativa (Brassicaceae)
The methionine chain elongation pathway in the biosynthesis of glucosinolates in Eruca sativa (Brassicaceae)
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DOI：
10.1006/abbi.2000.1812
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发表时间：
2000-06-15
影响因子：
3.9
通讯作者：
Gershenzon, J
中科院分区：
文献类型：
--
作者：
Graser, G;Schneider, B;Gershenzon, J
芥子油苷是含氮和硫的植物天然产物，作为风味前体、癌症预防剂和作物保护剂，在人类事务中变得越来越重要。虽然许多芥子油苷是在常见氨基酸之前生物合成的，但经济上重要的十字花科物种（如甘蓝型油菜）中的主要芥子油苷被认为是由甲硫氨酸或苯丙氨酸的链延长衍生物形成的。我们研究了芥菜中参与芥子油苷生物合成的蛋氨酸的链延长途径。将同位素标记的蛋氨酸和乙酸盐施用到切下的叶子上，并通过 MS 和 NMR 分析主要产物 4-甲硫基丁基芥子油苷（作为其脱硫衍生物分离）。 [U-C-13]甲硫氨酸的施用表明，该氨基酸的整个碳骨架（COOH碳除外）作为一个单元并入4MTB中。 [C-13]-和[C-14]乙酸盐的施用给出了与三步链延长循环的操作一致的标记模式，该循环通过乙酰辅酶A与衍生自甲硫氨酸的2-含氧酸缩合，并以氧化脱羧作用结束，形成带有一个额外亚甲基的新2-含氧酸。 [N-15]甲硫氨酸的施用提供了氨基基团转移至链延长的2-含氧酸的证据，形成延长的氨基酸，其充当硫代葡萄糖苷生物合成的剩余步骤的底物。产品中保留高水平的 N-15 表明氨基转移反应和链延伸循环位于同一亚细胞区室中，(C) 2000 学术出版社。
Glucosinolates are nitrogen- and sulfur-containing plant natural products that have become increasingly important in human affairs as flavor precursors, cancer-prevention agents, and crop protectants. While many glucosinolates are biosynthesized front common amino acids, the major glucosinolates in economically important species of the Brassicaceae, such as Brassica napus (oilseed rape), are thought to be formed from chain-elongated derivatives of methionine or phenylalanine. We investigated the chain elongation pathway for methionine that is involved in glucosinolate biosynthesis in Eruca sativa. Isotopically labeled methionine and acetate were administered to cut leaves and the major product, 4-methylthiobutylglucosinolate (isolated as its desulfated derivative), was analyzed by MS and NMR. Administration of [U-C-13]methionine showed that the entire carbon skeleton of this amino acid, with the exception of the COOH carbon, is incorporated as a unit into 4MTB. Administration of [C-13]- and [C-14]acetate gave a labeling pattern consistent with the operation of a three-step chain elongation cycle which beans with the condensation of acetyl-CoA with a 2-oxo acid derived from methionine and ends with an oxidative decarboxylation forming a new 2-oxo acid with one additional methylene group. Administration of [N-15]methionine provided evidence for the transfer of an amino group to the chain-elongated 2-oxo acid, forming an extended amino acid which serves as a substrate for the remaining steps of glucosinolate biosynthesis. The retention of a high level of N-15 in the products suggests that the amino transfer reactions and the chain elongation cycle are localized in the same subcellular compartment, (C) 2000 Academic Press.