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  • Title: Characterization of two beta-carotene ketolases, CrtO and CrtW, by complementation analysis in Escherichia coli.
    Author: Choi SK, Harada H, Matsuda S, Misawa N.
    Journal: Appl Microbiol Biotechnol; 2007 Jul; 75(6):1335-41. PubMed ID: 17415558.
    Abstract:
    The pathways from beta-carotene to astaxanthin are crucial key steps for producing astaxanthin, one of industrially useful carotenoids, in heterologous hosts. Two beta-carotene ketolases (beta-carotene 4,4'-oxygenase), CrtO and CrtW, with different structure are known up to the present. In this paper, we compared the catalytic functions of a CrtO ketolase that was obtained from a marine bacterium Rhodococcus erythropolis strain PR4, CrtO derived from cyanobacterium Synechosistis sp. PCC6803, and CrtW derived from a marine bacterium Brevundimonas sp. SD212, by complementation analysis in Escherichia coli expressing the known crt genes. Results strongly suggested that a CrtO-type ketolase was unable to synthesize astaxanthin from zeaxanthin, i.e., only a CrtW-type ketolase could accept 3-hydroxy-beta-ionone ring as the substrate. Their catalytic efficiency for synthesizing canthaxanthin from beta-carotene was also examined. The results obtained up to the present clearly suggest that the bacterial crtW and crtZ genes are a combination of the most promising gene candidates for developing recombinant hosts that produce astaxanthin as the predominant carotenoid.
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