Functional analysis of the beta and epsilon lycopene cyclase enzymes of Arabidopsis reveals a mechanism for control of cyclic carotenoid formation
Functional analysis of the beta and epsilon lycopene cyclase enzymes of Arabidopsis reveals a mechanism for control of cyclic carotenoid formation
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DOI：
10.2307/3870254
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发表时间：
1996-09-01
期刊：
影响因子：
11.6
通讯作者：
Gantt, E
中科院分区：
文献类型：
--
作者：
Cunningham, FX;Pogson, B;Gantt, E
具有环端基团的类胡萝卜素是所有植物、藻类和蓝藻的光合膜的重要组成部分。这些脂溶性化合物防止光氧化，为光合作用收集光，并消散天线色素吸收的多余光能。番茄红素（psi，psi-胡萝卜素）的环化是类胡萝卜素生物合成途径中的关键分支点。在高等植物类胡萝卜素中发现了两种类型的环端基团：β环和ε环。具有两个环的类胡萝卜素普遍存在，具有一个环和一个环的类胡萝卜素很常见；然而，具有两个ε环的类胡萝卜素是罕见的。我们已经在拟南芥中鉴定并测序了编码催化这两个环形成的酶的cdna。这些环化酶和环化酶是由相关的单拷贝基因编码的，这两种酶都使用线性对称的番茄红素作为底物。然而，epsilon环化酶只增加一个环，形成单环-胡萝卜素（epsilon，psi-胡萝卜素），而β环化酶在番茄红素的两端引入一个环，形成双环-胡萝卜素（epsilon， β -胡萝卜素）。当结合时，β和ε环化酶将番茄红素转化为α -胡萝卜素（β， ε -胡萝卜素），一种具有一个β环和一个ε环的类胡萝卜素。epsilon环化酶不能催化第二个epsilon环的引入，揭示了在植物和藻类中可以控制和调节β、β -和β、epsilon-类胡萝卜素的产生和比例，同时避免不适当的epsilon、epsilon-类胡萝卜素的形成的机制。
Carotenoids with cyclic end groups are essential components of the photosynthetic membranes in all plants, algae, and cyanobacteria. These lipid-soluble compounds protect against photooxidation, harvest light for photosynthesis, and dissipate excess light energy absorbed by the antenna pigments. The cyclization of lycopene (psi,psi-carotene) is a key branch point in the pathway of carotenoid biosynthesis. Two types of cyclic end groups are found in higher plant carotenoids: the beta and epsilon rings. Carotenoids with two beta rings are ubiquitous, and those with one beta and one epsilon ring are common; however, carotenoids with two epsilon rings are rare. We have identified and sequenced cDNAs that encode the enzymes catalyzing the formation of these two rings in Arabidopsis. These beta and epsilon cyclases are encoded by related, single-copy genes, and both enzymes use the linear, symmetrical lycopene as a substrate. However, the epsilon cyclase adds only one ring, forming the monocyclic delta-carotene (epsilon,psi-carotene), whereas the beta cyclase introduces a ring at both ends of lycopene to form the bicyclic beta-carotene (epsilon,beta-carotene). When combined, the beta and epsilon cyclases convert lycopene to alpha-carotene (beta,epsilon-carotene), a carotenoid with one beta and one epsilon ring. The inability of the epsilon cyclase to catalyze the introduction of a second epsilon ring reveals the mechanism by which production and proportions of beta,beta- and beta,epsilon-carotenoids may be controlled and adjusted in plants and algae, while avoiding the formation of the inappropriate epsilon,epsilon-carotenoids.