Mikkelsen M D, Hansen C H, Wittstock U, Halkier B A
Plant Biochemistry Laboratory, Department of Plant Biology, and Center for Molecular Plant Physiology (Place), The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark.
J Biol Chem. 2000 Oct 27;275(43):33712-7. doi: 10.1074/jbc.M001667200.
Glucosinolates are natural plant products known as flavor compounds, cancer-preventing agents, and biopesticides. We report cloning and characterization of the cytochrome P450 CYP79B2 from Arabidopsis. Heterologous expression of CYP79B2 in Escherichia coli shows that CYP79B2 catalyzes the conversion of tryptophan to indole-3-acetaldoxime. Recombinant CYP79B2 has a K(m) of 21 microm and a V(max) of 7.78 nmol/h/ml culture. Inhibitor studies show that CYP79B2 is different from a previously described enzyme activity that converts tryptophan to indole-3-acetaldoxime (Ludwig-Müller, J. , and Hilgenberg, W. (1990) Phytochemistry, 29, 1397-1400). CYP79B2 is wound-inducible and expressed in leaves, stem, flowers, and roots, with the highest expression in roots. Arabidopsis overexpressing CYP79B2 has increased levels of indole glucosinolates, which strongly indicates that CYP79B2 is involved in indole glucosinolate biosynthesis. Our data show that oxime production by CYP79s is not restricted to those amino acids that are precursors for cyanogenic glucosides. Our data are consistent with the hypothesis that indole glucosinolates have evolved from cyanogenesis. Indole-3-acetaldoxime is a precursor of the plant hormone indole-3-acetic acid, which suggests that CYP79B2 might function in biosynthesis of indole-3-acetic acid. Identification of CYP79B2 provides an important tool for modification of the indole glucosinolate content to improve nutritional value and pest resistance.
硫代葡萄糖苷是天然植物产物，被认为是风味化合物、防癌剂和生物杀虫剂。我们报道了从拟南芥中克隆细胞色素P450 CYP79B2并对其进行表征。CYP79B2在大肠杆菌中的异源表达表明，CYP79B2催化色氨酸转化为吲哚 - 3 - 乙醛肟。重组CYP79B2的米氏常数（K(m)）为21微摩尔，最大反应速度（V(max)）为7.78纳摩尔/小时/毫升培养物。抑制剂研究表明，CYP79B2与先前描述的将色氨酸转化为吲哚 - 3 - 乙醛肟的酶活性不同（路德维希 - 米勒，J.，和希尔根贝格，W.（1990年）《植物化学》，29，1397 - 1400）。CYP79B2受创伤诱导，在叶、茎、花和根中表达，在根中的表达量最高。过表达CYP79B2的拟南芥中吲哚硫代葡萄糖苷水平升高，这强烈表明CYP79B2参与吲哚硫代葡萄糖苷的生物合成。我们的数据表明，CYP79s产生肟并不局限于那些作为生氰糖苷前体的氨基酸。我们的数据与吲哚硫代葡萄糖苷从生氰作用进化而来的假说一致。吲哚 - 3 - 乙醛肟是植物激素吲哚 - 3 - 乙酸的前体，这表明CYP79B2可能在吲哚 - 3 - 乙酸的生物合成中起作用。CYP79B2的鉴定为改变吲哚硫代葡萄糖苷含量以提高营养价值和抗虫性提供了重要工具。
