61. ブラシノステロイドC-23位水酸化酵素の酵素学的解析

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Brassinosteroids (BRs) are plant steroid hormones that are essential for normal plant growth and development. Cytochrome P450 monooxygenases (P450s) play crucial roles in BR biosynthesis from campesterol to brassinolide, in which many oxygenations at steroidal skeleton and side-chain structure occur. Recent molecular genetic studies for BR-deficient mutants of Arabidopsis, rice, tomato and garden pea have identified several P450 genes (CYP85A, 90A, 90B, 90C, 90D, and 724B) so far. Among the BR-biosynthetic P450 genes, only CYP85As have been characterized by functional expression in yeast cells, revealing that these enzymes catalyze the C-6 oxidations. Recently, we have characterized CYP90B1 functionally expressed in E. coli and found that CYP90B1 predominantly catalyzes the C-22 hydroxylation of campesterol in the early C-22 hydroxylation pathway. Here, we report biochemical characterization of a P450, C-23 hydroxylase. The P450 was expressed in insect cells using a baculovirus expression system. The P450 activity was measured in an in vitro assay reconstituted with NADPH : cytochrome P450 reductase, and the reaction products were analyzed by GC-MS. The P450 catalyzed the C-23 hydroxylation of 6-deoxocathasterone and cathasterone to 6-deoxoteasterone and teasterone, respectively. We have also determined the substrate specificity of the C-23 hydroxylase. To our knowledge, this is the first report of the biochemical characterization of the C-23 hydroxylation by the P450.
植物化学調節学会の論文
2005-10-13

61. ブラシノステロイドC-23位水酸化酵素の酵素学的解析

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