A study in scarlet:: enzymes of ketocarotenoid biosynthesis in the flowers of Adonis aestivalis
A study in scarlet:: enzymes of ketocarotenoid biosynthesis in the flowers of Adonis aestivalis
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DOI：
10.1111/j.1365-313x.2004.02309.x
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发表时间：
2005-02-01
期刊：
影响因子：
7.2
通讯作者：
Gantt, E
中科院分区：
文献类型：
--
作者：
Cunningham, FX;Gantt, E
红色类酮胡萝卜素虾青素（3,3'-二羟基-4,4'-二酮- β， β -胡萝卜素）被广泛用作鱼类和甲壳类动物色素沉着的饲料添加剂，也经常被包含在人类营养补充剂中。人们对开发一种基于植物的生物生产工艺来生产这种有价值的类胡萝卜素非常感兴趣。毛茛科植物阿多尼斯（Adonis aestivalis）在植物中合成和积累大量虾青素和其他类酮胡萝卜素是罕见的。虾青素的形成只需要在玉米黄质每个β环的4号碳上添加一个羰基（3,3'-二羟基- β， β -胡萝卜素），这是一种通常存在于高等植物绿色组织中的类胡萝卜素。我们筛选了A. aestivalis花文库，以鉴定可能编码催化羰基添加酶的cdna。在这个筛选中选择的两个密切相关的cdna被发现指定的多肽序列与植物β -胡萝卜素3-羟化酶相似，酶将β -胡萝卜素（β， β -胡萝卜素）转化为玉米黄质。然而，当以β -胡萝卜素为底物时，Adonis酶在大肠杆菌中既不表现出4-酮酶活性，也不表现出3-羟化酶活性。相反，阿多尼斯cdna的产物被发现以两种截然不同的方式修饰β环：3,4位的去饱和和4号碳的羟基化。在大肠杆菌中形成的4-羟基类胡萝卜素被缓慢代谢为具有类酮胡萝卜素样吸收光谱的化合物。有人提出，4-羟基化后的3,4-去饱和导致4-酮- β环通过间接和意想不到的途径形成：酮-烯醇互变异构。
The red ketocarotenoid astaxanthin (3,3'-dihydroxy-4,4'-diketo-beta,beta-carotene) is widely used as an additive in feed for the pigmentation of fish and crustaceans and is frequently included in human nutritional supplements as well. There is considerable interest in developing a plant-based biological production process for this valuable carotenoid. Adonis aestivalis (Ranunculaceae) is unusual among plants in synthesizing and accumulating large amounts of astaxanthin and other ketocarotenoids. The formation of astaxanthin requires only the addition of a carbonyl at the number 4 carbon of each beta-ring of zeaxanthin (3,3'-dihydroxy-beta,beta-carotene), a carotenoid typically present in the green tissues of higher plants. We screened an A. aestivalis flower library to identify cDNAs that might encode the enzyme that catalyzes the addition of the carbonyls. Two closely related cDNAs selected in this screen were found to specify polypeptides similar in sequence to plant beta-carotene 3-hydroxylases, enzymes that convert beta-carotene (beta,beta-carotene) into zeaxanthin. The Adonis enzymes, however, exhibited neither 4-ketolase nor 3-hydroxylase activity when presented with beta-carotene as the substrate in Escherichia coli. Instead, the products of the Adonis cDNAs were found to modify beta-rings in two distinctly different ways: desaturation at the 3,4 position and hydroxylation of the number 4 carbon. The 4-hydroxylated carotenoids formed in E. coli were slowly metabolized to yield compounds with ketocarotenoid-like absorption spectra. It is proposed that a 3,4-desaturation subsequent to 4-hydroxylation of the beta-ring leads to the formation of a 4-keto-beta-ring via an indirect and unexpected route: a keto-enol tautomerization.