25 環状モノテルペノイド類の生合成 : C_<10>-プレニル鎖の環化機構(口頭発表の部)

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"Monoterpene cyclase" responsible for the cyclization of acyclic allylic pyrophosphate was isolated from the leaves of Mentha spicata and purified about 54-fold by chromatography on a Sephadex G-200 column following by a DEAE-cellulose column. Bivalent metal cations, especially manganese ion, was essential for the formation of allylic cations for the enzymatic cyclization. On the basis of the potential energy of the allylic cations, a reaction path from geranyl pyrophosphate (GPP) to cyclic monoterpenoids was predicted ; this shows that linalyl cation is a preferred intermediate for cyclization of the C_<10>-prenyl chain. Linalyl cation in the process of the enzymatic cyclization was confirmed by conversion of (+)-linalyl pyrophosphate (LPP) to (-)-limonene with the "monoterpene cyclase". Examination of the affinity of several substrates to the "monoterpene cyclase" by means of the UV difference spectrum indicates that the "monoterpene cyclase" can recognize the pyrophosphate moiety and the chain-length and enantiomeric structure of the hydrophobic moiety. In the biosynthesis of cyclic monoterpenoids from C_<10>-prenyl chain precursors by their cyclization, thus, it has been elucidated that GPP is first bound to the active site of the "monoterpene cyclase" with a bivalent metal ion. GPP bound to the active sites is transformed to linalyl cation by pulling out its pyrophosphate moiety with the bivalent metal ion and then the linalyl cation stereospecifically cyclizes to cyclic monoterpenoids under the steric control characteristic of the respective plants.
天然有機化合物討論会の論文
1987-07-25

25 環状モノテルペノイド類の生合成 : C_<10>-プレニル鎖の環化機構(口頭発表の部)

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