Reaction: (1) zeaxanthin + 2 reduced acceptor + 2 O2 = adonixanthin + 2 acceptor + 3 H2O
(2) adonixanthin + 2 reduced acceptor + 2 O2 = (3S,3'S)-astaxanthin + 2 acceptor + 3 H2O
For diagram of reaction click here.
Glossary: zeaxanthin = β,β-carotene-3,3'-diol
adonixanthin = 3,3'-dihydroxy-β,β-carotene-4-one
(3S,3'S)-astaxanthin = (3S,3'S)-3,3'-dihydroxy-β,β-carotene-4,4'-dione
Other name(s): BKT (ambiguous); crtW148 (gene name)
Systematic name: zeaxanthin,donor:oxygen oxidoreductase (adonixanthin-forming)
Comments: The enzyme has a similar activity to that of EC 18.104.22.168, β-carotene 4-ketolase, but unlike that enzyme is able to also act on zeaxanthin.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
1. Zhong, Y.J., Huang, J.C., Liu, J., Li, Y., Jiang, Y., Xu, Z.F., Sandmann, G. and Chen, F. Functional characterization of various algal carotenoid ketolases reveals that ketolating zeaxanthin efficiently is essential for high production of astaxanthin in transgenic Arabidopsis. J. Exp. Bot. 62 (2011) 3659-3669. [PMID: 21398427]
2. Huang, J., Zhong, Y., Sandmann, G., Liu, J. and Chen, F. Cloning and selection of carotenoid ketolase genes for the engineering of high-yield astaxanthin in plants. Planta 236 (2012) 691-699. [PMID: 22526507]