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首页> 外文期刊>Journal of Experimental Botany >Biosynthesis of a cholesterol-derived brassinosteroid, 28-norcastasterone, in Arabidopsis thaliana
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Biosynthesis of a cholesterol-derived brassinosteroid, 28-norcastasterone, in Arabidopsis thaliana

机译：拟南芥中胆固醇衍生的油菜素类固醇28-去甲甾体的生物合成

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A metabolic study revealed that 28-norcastasterone in Arabidopsis is synthesized from cholesterol via the late C-6 oxidation pathway. On the other hand, the early C-6 oxidation pathway was found to be interrupted because cholestanol is converted to 6-oxocholestanol, but further metabolism to 28-norcathasterone was not observed. The 6-oxoBRs were found to have been produced from the respective 6-deoxoBRs administered to the enzyme solution, thus indicating that these 6-oxoBRs are supplied from the late C-6 oxidation pathway. Heterologously expressed CYP85A1 and CYP85A2 in yeast catalysed this C-6 oxidation, with CYP85A2 being much more efficient than CYP85A1. Abnormal growth of det2 and dwf4 was restored via the application of 28-norcastasterone and closer precursors. Furthermore, det2 and dwf4 could not convert cholesterol to cholestanol and cholestanol to 6-deoxo-28-norcathasterone, respectively. It is, therefore, most likely that the same enzyme system is operant in the synthesis of both 28-norcastasterone and castasterone. In the presence of S-adenosyl-L-methionine, the cell-free enzyme extract catalysed the C-24 methylation of 28-norcastasterone to castasterone, although the conversion rates of 28-norteasterone to teasterone and 28-nortyphasterol to typhasterol were much lower; this suggests that 28-norcastasterone is the primary precursor for the generation of C28-BRs from C27-BRs.
机译：一项代谢研究显示，拟南芥中的28-去甲甾酮是通过晚期C-6氧化途径由胆固醇合成的。另一方面，发现早期的C-6氧化途径被中断，因为胆甾醇被转化为6-氧胆甾醇，但是未观察到进一步代谢为28-正十八烷酮。发现6-氧代BR是从分别施用给酶溶液的6-脱氧-BR中产生的，因此表明这些6-氧代BR是由后期的C-6氧化途径提供的。酵母中异源表达CYP85A1和CYP85A2催化了这种C-6氧化，其中CYP85A2比CYP85A1更有效。通过使用28-去甲甾酮和更接近的前体，恢复了det2和dwf4的异常生长。此外，det2和dwf4不能分别将胆固醇转化为胆固醇和胆固醇转化为6-deoxo-28-norcathasterone。因此，最有可能的是，相同的酶系统在28-去甲甾烷酮和蓖麻甾酮的合成中都起作用。在S-腺苷-L-蛋氨酸的存在下，无细胞酶提取物催化了28-去甲甾烯酮转化为Castasterone的C-24甲基化，尽管28-去甲甾酮转化为茶甾酮和28-去甲甾醇转化为邻苯二酚的转化率要低得多。 ;这表明28-去甲甾烷酮是从C 27 -BRs生成C 28 -BRs的主要前体。

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