7 ラノステロールを経由する植物ステロール新規生合成経路(口頭発表の部)

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Sterols are important as structural components of plasma membranes and precursors of steroidal hormones in both animals and plants. The differences in the biosynthesis of sterols between plants and animals are believed to begin at the step of cyclization of oxidosqualene, which is cyclized to lanosterol in animals and to cycloartenol in plants. Last year, three laboratories independently identified lanosterol synthase genes from dicotyledonous plant species including Arabidopsis, Panax, and Lotus. As for Arabidopsis lanosterol synthase (LAS1), in planta function was demonstrated through overexpression of LAS1 in transgenic plant cells. From these results, it was elucidated that plants have two routes of the steroidal backbone synthesis. It is important to understand whether biosynthetic pathway of phytosterols via lanosterol generally exists or not. To answer this question, we designed a tracer experiment using [6-^<13>C^2H_3]mevalonate. By the elucidation of deuterium on C-19 behavior of phytosterol, it is possible to clarify that phytosterol is biosynthesized via either cycloartenol or lanosterol; two deuterium retained and three deuterium retained phytosterol are biosynthesized via cycloartenol and lanosterol, respectively. The number of deuterium can be analyzed by ^<13>C-NMR; carbon spectrum connected a deuterium will be theoretically shifted to approximately 0.3ppm up-field by isotope effect. According to this stratagy, [6-^<13>C^2H_3]rnevalonate was synthesized and fed to the seedlings of wild type and LAS1 overexpression plant of Arabidopsis. To enhance the incorporation ratio of the labeled mevalonate, lovastatin (inhibitor of HMG-CoA reductase) was applied at the same time. After incubation, extracted sitosterols were analyzed by ^1H, ^2H-double decoupled ^<13>C-NMR. Although main peak was two deuterium-retained peak, three deuteriums retained peak was observed as minor peak. The peak intensity of sitosterol in LAS1 overexpression was approximately three times as strong as that in WT. This is the first direct evidence that the biosynthetic pathway of phytosterol via lanosterol existed in plant cells.
天然有機化合物討論会の論文
2007-08-24

7 ラノステロールを経由する植物ステロール新規生合成経路(口頭発表の部)

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