Breitenbach J, Misawa N, Kajiwara S, Sandmann G
Biosynthesis Group, Botanical Institute, J.W. Goethe Universität, Frankfurt, Germany.
FEMS Microbiol Lett. 1996 Jul 1;140(2-3):241-6. doi: 10.1016/0378-1097(96)00187-5.
High level expression of the functional beta-carotene ketolase gene bkt from Haematococcus pluvialis occurred in Escherichia coli transformants producing beta-carotene or zeaxanthin as a result of the presence of additional carotenoid genes from Erwinia uredovora. Requirement of molecular oxygen for the insertion of the keto group was demonstrated. The final product of this two-step ketolase reaction from beta-carotene is canthaxanthin (4,4'-diketo-beta-carotene) with the 4-monoketo derivative echinenone as an intermediate. A reaction sequence for the formation of astaxanthin from beta-carotene was established based on kinetic data on astaxanthin formation in E. coli transformants carrying the hydroxylase gene crtZ from Erwinia along with bkt. We conclude that the carotenoids zeaxanthin and adonixanthin which accumulate in addition to astaxanthin in this transformant are products of side reactions rather than direct precursors of astaxanthin. The possible mechanisms for the formation of the keto derivatives are discussed.
由于存在来自丁香假单胞菌的额外类胡萝卜素基因，雨生红球藻功能性β-胡萝卜素酮醇酶基因bkt在产生β-胡萝卜素或玉米黄质的大肠杆菌转化体中实现了高水平表达。证明了分子氧对于酮基插入的必要性。该两步酮醇酶反应从β-胡萝卜素生成的最终产物是虾青素（4,4'-二酮-β-胡萝卜素），4-单酮衍生物海胆酮作为中间体。基于携带来自丁香假单胞菌的羟化酶基因crtZ以及bkt的大肠杆菌转化体中虾青素形成的动力学数据，建立了从β-胡萝卜素形成虾青素的反应序列。我们得出结论，在该转化体中除虾青素外积累的类胡萝卜素玉米黄质和阿多尼黄质是副反应的产物，而非虾青素的直接前体。讨论了酮衍生物形成的可能机制。
