IUBMB Enzyme Nomenclature


Accepted name: zeaxanthin 4-ketolase

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, 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]

[EC created 2018]

Return to EC 1.14.99 home page
Return to EC 1.14 home page
Return to EC 1 home page
Return to Enzymes home page
Return to IUBMB Biochemical Nomenclature home page