32
S. Takaichi
2.3.3.3 Algae
Little is known about the carotenogenic pathways among algae, but some theories
have been proposed based on the chemical structures of carotenoids (Fig. 2.2). Functionally confirmed enzymes have been reported mainly in Chlorophyceae including
Chlorella, Chlamydomonas, Dunaliella, and Haematococcus for CrtB, CrtP, CrtL-b,
CrtR-b, Zep, Vde, and CrtW (Table 2.2) (Takaichi 2011).
In the cell-free preparation of Amphidinium carterae (Dinophyta),
14 C-labellled
zeaxanthin was incorporated into allenic neoxanthin, and then into acetylenic diadinoxanthin and C 37 peridinin (Fig. 2.2). In addition, the three carbon atoms C13
,14
,20
of peridinin were eliminated from neoxanthin (C-13,14,20) (Swift and
Milborrow 1981; Swift et al. 1982). In terms of organic chemistry, the C-7,8 double
bond of zeaxanthin can be oxidized to the triple bond (acetylenic group) of alloxanthin (Britton 1998). Consequently, alloxanthin in Cryptophyta may be synthesized
from zeaxanthin, since no epoxy carotenoids exist (Table 2.1). Diadinoxanthin and
diatoxanthin may be synthesized via neoxanthin, as they are asymmetric structures
(Figs. 2.1 and 2.2).
Allenic carotenoids are very limited in algae. From their chemical structures,
all-trans neoxanthin might be converted to fucoxanthin, dinoxanthin, peridinin,
vaucheriaxanthin, and diadinoxanthin, but the pathways and enzymes remain
unknown (Figs. 2.1 and 2.2).
Under stressful conditions, such as high light, UV irradiation, or nutrition stress,
some of the Chlorophyceae including Haematococcus, Chlorella, and Scenedesmus,
accumulate ketocarotenoids, canthaxanthin, and astaxanthin, which are synthesized
by combining CrtR-b and β-carotene ketolase (CrtW, BKT) (Table 2.2) (Kajiwara
et al. 1995; Lotan and Hirschberg 1995; Huang 2006a, b; Lemoine and Schoefs 2010).
Note that although β-carotene ketolase of Haematococcus and Chlorella were named
CrtO at first (Huang 2006a, b), they are the CrtW-type, not the CrtO-type, according
to the amino acid sequences (Table 2.2).
2.3.4 α-Carotene Derivatives and Their Synthesis
In Arabidopsis thaliana, β-carotene is hydroxylated mainly by the non-heme diiron enzymes, BCH1 and BCH2 (CrtR-b), to produce zeaxanthin, while α-carotene
is mainly hydroxylated by the cytochrome P450 enzymes, CYP97A3 for the β-end
group and CYP97C1 for the β- and ε-end groups, to produce lutein (Kim et al. 2009).
In Porphyra umbilicalis, β-carotene hydroxylase of CYP97 has been functionally
confirmed (Yang et al. 2014) (Table 2.2).
Lutein and its derivatives are found only in the Rhodophyta (LUT-type), Cryptophyta, Euglenophyta, Chlorarachniophyta, and Chlorophyta (Table 2.1), but no
details have yet been confirmed about the hydroxylation of α-carotene. From the
S. Takaichi
2.3.3.3 Algae
Little is known about the carotenogenic pathways among algae, but some theories
have been proposed based on the chemical structures of carotenoids (Fig. 2.2). Functionally confirmed enzymes have been reported mainly in Chlorophyceae including
Chlorella, Chlamydomonas, Dunaliella, and Haematococcus for CrtB, CrtP, CrtL-b,
CrtR-b, Zep, Vde, and CrtW (Table 2.2) (Takaichi 2011).
In the cell-free preparation of Amphidinium carterae (Dinophyta),
14 C-labellled
zeaxanthin was incorporated into allenic neoxanthin, and then into acetylenic diadinoxanthin and C 37 peridinin (Fig. 2.2). In addition, the three carbon atoms C13
,14
,20
of peridinin were eliminated from neoxanthin (C-13,14,20) (Swift and
Milborrow 1981; Swift et al. 1982). In terms of organic chemistry, the C-7,8 double
bond of zeaxanthin can be oxidized to the triple bond (acetylenic group) of alloxanthin (Britton 1998). Consequently, alloxanthin in Cryptophyta may be synthesized
from zeaxanthin, since no epoxy carotenoids exist (Table 2.1). Diadinoxanthin and
diatoxanthin may be synthesized via neoxanthin, as they are asymmetric structures
(Figs. 2.1 and 2.2).
Allenic carotenoids are very limited in algae. From their chemical structures,
all-trans neoxanthin might be converted to fucoxanthin, dinoxanthin, peridinin,
vaucheriaxanthin, and diadinoxanthin, but the pathways and enzymes remain
unknown (Figs. 2.1 and 2.2).
Under stressful conditions, such as high light, UV irradiation, or nutrition stress,
some of the Chlorophyceae including Haematococcus, Chlorella, and Scenedesmus,
accumulate ketocarotenoids, canthaxanthin, and astaxanthin, which are synthesized
by combining CrtR-b and β-carotene ketolase (CrtW, BKT) (Table 2.2) (Kajiwara
et al. 1995; Lotan and Hirschberg 1995; Huang 2006a, b; Lemoine and Schoefs 2010).
Note that although β-carotene ketolase of Haematococcus and Chlorella were named
CrtO at first (Huang 2006a, b), they are the CrtW-type, not the CrtO-type, according
to the amino acid sequences (Table 2.2).
2.3.4 α-Carotene Derivatives and Their Synthesis
In Arabidopsis thaliana, β-carotene is hydroxylated mainly by the non-heme diiron enzymes, BCH1 and BCH2 (CrtR-b), to produce zeaxanthin, while α-carotene
is mainly hydroxylated by the cytochrome P450 enzymes, CYP97A3 for the β-end
group and CYP97C1 for the β- and ε-end groups, to produce lutein (Kim et al. 2009).
In Porphyra umbilicalis, β-carotene hydroxylase of CYP97 has been functionally
confirmed (Yang et al. 2014) (Table 2.2).
Lutein and its derivatives are found only in the Rhodophyta (LUT-type), Cryptophyta, Euglenophyta, Chlorarachniophyta, and Chlorophyta (Table 2.1), but no
details have yet been confirmed about the hydroxylation of α-carotene. From the