Non-specific biosynthesis of gammacerane derivatives by a cell-free system from the protozoon Tetrahymena pyriformis. Conformations of squalene, (3S)-squalene epoxide and (3R)-squalene epoxide during the cyclization.
Non-specific biosynthesis of gammacerane derivatives by a cell-free system from the protozoon Tetrahymena pyriformis. Conformations of squalene, (3S)-squalene epoxide and (3R)-squalene epoxide during the cyclization.
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由原生动物梨形四膜虫的无细胞系统非特异性生物合成伽玛蜡烷衍生物。
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
G. Ourisson
中科院分区：
文献类型：
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作者：
P. Bouvier;Y. Berger;M. Rohmer;G. Ourisson
1. 将来自梨形四膜虫的无细胞系统与[12-3H]角鲨烯或(RS)-2,3-环氧-2,3-二氢-[12,13-3H]角鲨烯一起孵育。角鲨烯环化为四海马醇，而外消旋角鲨烯环氧化物转化为γcerane-3α,21α-二醇和γcerane-3β,21α-二醇。 (RS)-2,3-环氧-2,3-二氢-[3-3H]角鲨烯环化后，两种差向异构γ蜡二醇均用位于C-3的氚原子标记，表明没有发生通过3-氧代化合物的异构化。 2. 合成的(2E,22E)-(1,1,1,24,24,24-2H6)角鲨烯和(RS)-(22E)-2,3-环氧-2,3-二氢-(1,1,1,24,24,24-2H6)角鲨烯环化产物的质子核磁共振谱表明角鲨烯及其(3S)对映体环氧化物以全前椅构象环化，而角鲨烯环氧化物的 (3R) 对映体以循环 A 的前船构象环化。 3. 梨形角鲨烯环化酶与巴氏醋杆菌环化酶一样缺乏底物特异性：除了其正常底物角鲨烯外，它还环化其两种对映体。环氧化物。这种构象多样性是角鲨烯环化酶的特征，但在真核生物的角鲨烯环氧化物环化酶中不再存在。
1. A cell-free system from the protozoon Tetrahymena pyriformis was incubated with either [12-3H]squalene or (RS)-2,3-epoxy-2,3-dihydro-[12,13-3H]squalene. Squalene was cyclized into tetrahymanol whereas racemic squalene epoxide was transformed into gammacerane-3 alpha,21 alpha-diol and gammacerane-3 beta,21 alpha-diol. After cyclization of (RS)-2,3-epoxy-2,3-dihydro-[3-3H]squalene, both epimeric gammaceranediols were labelled with a tritium atom located at C-3, showing that no isomerization via a 3-oxo compound occurred. 2. The proton NMR spectra of the cyclization products of synthetic (2E, 22E)-(1,1,1,24,24,24-2H6)squalene and (RS)-(22E)-2,3-epoxy-2,3-dihydro-(1,1,1,24,24,24-2H6)squalene show that squalene and the (3S)enantiomer of its epoxide are cyclized in an all pre-chair conformation, whereas the (3R) enantiomer of squalene epoxide is cyclized in a pre-boat conformation as concerns the cycle A. 3. The squalene cyclase of T. pyriformis presents the same lack of substrate specificity as the cyclase of Acetobacter pasteurianum: in addition to squalene, its normal substrate, it also cyclizes both enantiomers of its epoxide. This conformational versatility is characteristic of squalene cyclases but no longer exists in the squalene epoxide cyclases from eukaryotes.