Studies on the Properties and Bio-Functions of Prenyl Epoxidase

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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.