Ginkgolide and bilobalide biosynthesis in Ginkgo biloba. II: Identification of a possible intermediate compound by using inhibitors of cytochrome P-45-dependent oxygenases.

摘要

Studies of G. biloba seedlings showed that diterpene hydrocarbons were present only in roots, as trace amounts (1-3 鎔 g-1 fresh weight). Dehydroabietane was the main hydrocarbon compound. Two inhibitors of cytochrome P-450-dependent oxygenases, tetcyclacis and clotrimazole, were supplied to the seedlings via the roots in order to deregulate the terpene pathway. As a result of the treatment, the ginkgolide and bilobalide content was lowered, both in roots and leaves. A treatment with 10 mM tetcyclacis was more effective than a 100 mM clotrimazole treatment and resulted in a significant increase (up to 41 times) of diterpene hydrocarbons in roots. This increase concerned primarily dehydroabietane. 14CO2 feeding experiments, following 10 鍹 tetcyclacis treatment, showed that only dehydroabietane was highly labelled. The absence of labelling in both ginkgolides and bilobalide indicated that the oxygenation reactions leading to the end-products were fully inhibited. These results support the existence of a precursor-product relationship between dehydroabietane and ginkgolides plus bilobalides. The biosynthesis of oxygenated terpenes in G. biloba proceeds via a hydrocarbon intermediate.