Bennett R. N., Kiddle G., Wallsgrove R. M.
Biochemistry and Physiology Department, IACR-Rothamsted, Harpenden AL5 2JQ, United Kingdom.
Plant Physiol. 1997 Aug;114(4):1283-1291. doi: 10.1104/pp.114.4.1283.
One of the first steps in glucosinolate biosynthesis is the conversion of amino acids to their aldoximes. The biochemistry of this process is controversial, and several very different enzyme systems have been described. The major glucosinolate in white mustard (Sinapis alba) is sinalbin, which is derived from tyrosine via its aldoxime, and this conversion is catalyzed by a cytochrome P450 (Cyt P450) monooxygenase. Phenylethyl- and alkenylglucosinolates are also present in white mustard leaves, as are the enzymes catalyzing the relevant aldoxime formation from homophenylalanine and methionine homologs, respectively. These enzymes are similar to those found in Brassica sp. and are distinct from the tyrosine-dependent enzyme in that they contain no heme and are unaffected by Cyt P450 inhibitors. They are instead inhibited by the flavoprotein inhibitor diphenylene iodonium and by Cu2+. In both white mustard and oilseed rape (Brassica napus) methyl jasmonate specifically stimulates indolylglucosinolate biosynthesis and yet has no effect on sinalbin accumulation in either cotyledons or leaves of white mustard. White mustard appears to be unique among crucifers in having a Cyt P450 aldoxime-forming enzyme for biosynthesis of one glucosinolate, although it also contains all of the non-Cyt P450 enzyme systems found in other members of the family. Sinalbin biosynthesis in white mustard is therefore an inappropriate model system for the synthesis of other glucosinolates in crucifers, including canola and oilseed rape.
硫代葡萄糖苷生物合成的最初步骤之一是氨基酸向其醛肟的转化。这一过程的生物化学存在争议，并且已经描述了几种非常不同的酶系统。白芥（Sinapis alba）中的主要硫代葡萄糖苷是白芥子硫苷，它通过其醛肟从酪氨酸衍生而来，这种转化由细胞色素P450（Cyt P450）单加氧酶催化。苯乙基硫代葡萄糖苷和烯基硫代葡萄糖苷也存在于白芥叶中，同时还存在分别催化从高苯丙氨酸和蛋氨酸同系物形成相关醛肟的酶。这些酶与在芸苔属植物中发现的酶相似，并且与酪氨酸依赖性酶不同，因为它们不含血红素且不受Cyt P450抑制剂的影响。相反，它们被黄素蛋白抑制剂二亚苯基碘鎓和Cu2+抑制。在白芥和油菜（Brassica napus）中，茉莉酸甲酯特异性地刺激吲哚基硫代葡萄糖苷的生物合成，但对白芥子硫苷在白芥子叶或叶片中的积累没有影响。白芥在十字花科植物中似乎是独特的，它具有一种用于一种硫代葡萄糖苷生物合成的Cyt P450醛肟形成酶，尽管它也含有该科其他成员中发现的所有非Cyt P450酶系统。因此，白芥中的白芥子硫苷生物合成对于十字花科植物中其他硫代葡萄糖苷的合成，包括油菜籽和油菜，不是一个合适的模型系统。
