The Enzyme Database

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Transferred entry: β-carotene 3-hydroxylase. Now EC, β-carotene 3-hydroxylase.
[EC created 2011, deleted 2017]
Accepted name: β-carotene 3-hydroxylase
Reaction: β-carotene + 4 reduced ferredoxin [iron-sulfur] cluster + 2 H+ + 2 O2 = zeaxanthin + 4 oxidized ferredoxin [iron-sulfur] cluster + 2 H2O (overall reaction)
(1a) β-carotene + 2 reduced ferredoxin [iron-sulfur] cluster + H+ + O2 = β-cryptoxanthin + 2 oxidized ferredoxin [iron-sulfur] cluster + H2O
(1b) β-cryptoxanthin + 2 reduced ferredoxin [iron-sulfur] cluster + H+ + O2 = zeaxanthin + 2 oxidized ferredoxin [iron-sulfur] cluster + H2O
Other name(s): β-carotene 3,3′-monooxygenase; CrtZ
Systematic name: β-carotene,reduced ferredoxin [iron-sulfur] cluster:oxygen 3-oxidoreductase
Comments: Requires ferredoxin and Fe(II). Also acts on other carotenoids with a β-end group. In some species canthaxanthin is the preferred substrate.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Sun, Z., Gantt, E. and Cunningham, F.X., Jr. Cloning and functional analysis of the β-carotene hydroxylase of Arabidopsis thaliana. J. Biol. Chem. 271 (1996) 24349–24352. [DOI] [PMID: 8798688]
2.  Fraser, P.D., Miura, Y. and Misawa, N. In vitro characterization of astaxanthin biosynthetic enzymes. J. Biol. Chem. 272 (1997) 6128–6135. [DOI] [PMID: 9045623]
3.  Fraser, P.D., Shimada, H. and Misawa, N. Enzymic confirmation of reactions involved in routes to astaxanthin formation, elucidated using a direct substrate in vitro assay. Eur. J. Biochem. 252 (1998) 229–236. [DOI] [PMID: 9523693]
4.  Bouvier, F., Keller, Y., d'Harlingue, A. and Camara, B. Xanthophyll biosynthesis: molecular and functional characterization of carotenoid hydroxylases from pepper fruits (Capsicum annuum L.). Biochim. Biophys. Acta 1391 (1998) 320–328. [DOI] [PMID: 9555077]
5.  Linden, H. Carotenoid hydroxylase from Haematococcus pluvialis: cDNA sequence, regulation and functional complementation. Biochim. Biophys. Acta 1446 (1999) 203–212. [DOI] [PMID: 10524195]
6.  Zhu, C., Yamamura, S., Nishihara, M., Koiwa, H. and Sandmann, G. cDNAs for the synthesis of cyclic carotenoids in petals of Gentiana lutea and their regulation during flower development. Biochim. Biophys. Acta 1625 (2003) 305–308. [DOI] [PMID: 12591618]
7.  Choi, S.K., Matsuda, S., Hoshino, T., Peng, X. and Misawa, N. Characterization of bacterial β-carotene 3,3′-hydroxylases, CrtZ, and P450 in astaxanthin biosynthetic pathway and adonirubin production by gene combination in Escherichia coli. Appl. Microbiol. Biotechnol. 72 (2006) 1238–1246. [DOI] [PMID: 16614859]
[EC created 2011 as EC, transferred 2017 to EC]
Accepted name: β-carotene 4-ketolase
Reaction: (1) β-carotene + 2 reduced acceptor + 2 O2 = echinenone + 2 acceptor + 3 H2O
(2) echinenone + 2 reduced acceptor + 2 O2 = canthaxanthin + 2 acceptor + 3 H2O
Glossary: echinenone = β,β-caroten-4-one
canthaxanthin = β,β-carotene-4,4′-dione
zeaxanthin = β,β-carotene-3,3′-diol
astaxanthin = 3,3′-dihydroxy-β,β-carotene-4,4′-dione
Other name(s): BKT (ambiguous); β-C-4 oxygenase; β-carotene ketolase; crtS (gene name); crtW (gene name)
Systematic name: β-carotene,donor:oxygen oxidoreductase (echinenone-forming)
Comments: The enzyme, studied from algae, plants, fungi, and bacteria, adds an oxo group at position 4 of a carotenoid β ring. It is involved in the biosynthesis of carotenoids such as astaxanthin and flexixanthin. The enzyme does not act on β rings that are hydroxylated at position 3, such as in zeaxanthin (cf. EC, zeaxanthin 4-ketolase). The enzyme from the yeast Xanthophyllomyces dendrorhous is bifuntional and also catalyses the activity of EC, β-carotene 3-hydroxylase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Lotan, T. and Hirschberg, J. Cloning and expression in Escherichia coli of the gene encoding β-C-4-oxygenase, that converts β-carotene to the ketocarotenoid canthaxanthin in Haematococcus pluvialis. FEBS Lett. 364 (1995) 125–128. [PMID: 7750556]
2.  Breitenbach, J., Misawa, N., Kajiwara, S. and Sandmann, G. Expression in Escherichia coli and properties of the carotene ketolase from Haematococcus pluvialis. FEMS Microbiol. Lett. 140 (1996) 241–246. [PMID: 8764486]
3.  Steiger, S. and Sandmann, G. Cloning of two carotenoid ketolase genes from Nostoc punctiforme for the heterologous production of canthaxanthin and astaxanthin. Biotechnol. Lett. 26 (2004) 813–817. [PMID: 15269553]
4.  Ojima, K., Breitenbach, J., Visser, H., Setoguchi, Y., Tabata, K., Hoshino, T., van den Berg, J. and Sandmann, G. Cloning of the astaxanthin synthase gene from Xanthophyllomyces dendrorhous (Phaffia rhodozyma) and its assignment as a β-carotene 3-hydroxylase/4-ketolase. Mol. Genet. Genomics 275 (2006) 148–158. [PMID: 16416328]
5.  Tao, L., Yao, H., Kasai, H., Misawa, N. and Cheng, Q. A carotenoid synthesis gene cluster from Algoriphagus sp. KK10202C with a novel fusion-type lycopene β-cyclase gene. Mol. Genet. Genomics 276 (2006) 79–86. [PMID: 16625353]
6.  Kathiresan, S., Chandrashekar, A., Ravishankar, G.A. and Sarada, R. Regulation of astaxanthin and its intermediates through cloning and genetic transformation of β-carotene ketolase in Haematococcus pluvialis. J. Biotechnol. 196-197 (2015) 33–41. [PMID: 25612872]
[EC created 2018]
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
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
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]

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