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.
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. [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. [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. [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. [PMID: 9555077]
5.  Linden, H. Carotenoid hydroxylase from Haematococcus pluvialis: cDNA sequence, regulation and functional complementation. Biochim. Biophys. Acta 1446 (1999) 203–212. [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. [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. [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.
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]