Studies on the Properties and Bio-Functions of Prenyl Epoxidase

灰霉病菌粗蛋白提取物与6-戊烯基柚皮苷(6-PN)孵育20小时后，催化7-O-甲基叶黄酮的戊烯基环氧化反应，生成的环氧化物在pH 7.5的缓冲溶液中被缓慢地非酶转化为相应的二氢呋喃衍生物。未经6-PN预孵育的菌丝体在6-PN存在下制备的无细胞提取物几乎不具有环氧化活性。这些事实表明，底物类似物6-PN的作用不是作为酶稳定剂，而是作为酶诱导剂。酶的反应依赖于双原子氧和NADPH。低剂量的FAD是获得最大酶活力所必需的。由于除一氧化碳和细胞色素c外，该酶不被几种细胞色素P-450抑制剂抑制，因此该酶似乎不属于依赖细胞色素P-450的单加氧酶，而属于依赖于FAD的单加氧酶。虽然125,000 g上清液中的酶活性约占总酶活力的一半，但125,000 g小球的环氧化反应比活力(x 3.7)高于可溶性部分。底物专一性也用不同位置和不同数目的异戊烯基异黄酮来检测。讨论了目前依赖于FAD的戊烯基黄酮环氧酶的一些性质，并与其他黄素蛋白单加氧酶和植物抗毒素环化酶进行了比较。除了这些研究结果外，还介绍了一篇综述文章《真菌代谢类黄酮和相关的植物防御素》，讨论了微生物和植物中异戊烯基黄酮代谢的生物学特性。

Crude protein extracts from Botrytis cinerea preincubated with 6-prenylnaringenin (6-PN) for 20 hr catalyzed the prenyl epoxidation of 7-O-methyl-luteone, The resulting epoxide was non-enzymatically and slowly converted into the corresponding dihydrofurano derivative in a buffer solution at pH 7.5. Preparation of cell-free extracts in the presence of 6-PN from the mycelia without preincubation with 6-PN hardly showed the epoxidizing activity. These facts revealed that the substrate analogue 6-PN took a role not as an enzyme stabilizer, but as an enzyme inducer. The enzyme reaction depends on diatomic oxygen and NADPH.Low amounts of FAD are necessary for maximal enzyme activity. Because the enzymatic activity was not inhibited by several inhibitors of cytochrome P-450 in addition to carbon monooxide and cytochrome c, this enzyme seems to belong not to the monooxygenase group dependent on cytochrome P-450, but to that dependent on FAD.Although about half of the total enzyme activity was found in the 125,000 g supernatant, the specific activity for the epoxidation reaction of 125,000 g pellets was higher (x 3.7) than that of the soluble fraction. Substrate specificity was also examined using someprenylisoflavones differing in position and number of prenyl substitution. Some properties of the present prenylflavonoid epoxidase dependent on FAD was discussed in comparison with otherflavoprotein monooxygenases and prenyl cyclization enzymes concerning phytoalexin biosynthesis.In addition to these research results, a review article "Fungal metabolism of flavonoids and related phytoalexins" was described to discuss the biological aspects of prenylated flavonoid metabolisms in microorganisms and plants.