2 Carotenoids in Phototrophic Microalgae …
25
Fig. 2.3 Carotenogenesis pathways and enzymes, whose functions are confirmed, in cyanobacteria
functions have been confirmed in algae, including cyanobacteria, are summarized in
Table 2.2. Unfortunately, these enzymes are mostly from cyanobacteria and green
algae.
2.3.1 Lycopene Synthesis
2.3.1.1 Isopentenyl Pyrophosphate to Phytoene Synthesis
Two independent pathways of isopentenyl pyrophosphate (IPP) synthesis exist: the
classical mevalonate (MVA) pathway and the alternative, non-mevalonate, 1-deoxyd-xylulose-5-phosphate (DOXP) pathway, which was identified in the 1990s (Lichtenthaler 1999; Eisenreich et al. 2004). In the MVA pathway, acetyl-Coenzyme A
is converted to IPP through mevalonate, and the enzymes and genes have been well
studied. The pathway is found in the plant cytoplasm, animals, and some bacteria
(Lichtenthaler 1999; Miziorko 2011). In DOXP pathway, pyruvate and glycelaldehyde are converted to IPP. The DOXP pathway is found in cyanobacteria, the plastids
of algae and land plants, and some bacteria (Lichtenthaler 1999). Carotenoids are
synthesized in plastids. Exceptionally, among oxygenic phototrophs, the Euglenophyceae demonstrate only the MVA pathway, and the Chlorophyceae demonstrate
only the DOXP pathway (Lichtenthaler 1999; Takaichi 2011).
All carotenoids in oxygenic phototrophs consist of eight IPP units. Farnesyl
pyrophosphate (C 15 ) is synthesized from three IPPs, after which one IPP is added to
farnesyl pyrophosphate by geranylgeranyl pyrophosphate synthase (CrtE, GGPS)
25
Fig. 2.3 Carotenogenesis pathways and enzymes, whose functions are confirmed, in cyanobacteria
functions have been confirmed in algae, including cyanobacteria, are summarized in
Table 2.2. Unfortunately, these enzymes are mostly from cyanobacteria and green
algae.
2.3.1 Lycopene Synthesis
2.3.1.1 Isopentenyl Pyrophosphate to Phytoene Synthesis
Two independent pathways of isopentenyl pyrophosphate (IPP) synthesis exist: the
classical mevalonate (MVA) pathway and the alternative, non-mevalonate, 1-deoxyd-xylulose-5-phosphate (DOXP) pathway, which was identified in the 1990s (Lichtenthaler 1999; Eisenreich et al. 2004). In the MVA pathway, acetyl-Coenzyme A
is converted to IPP through mevalonate, and the enzymes and genes have been well
studied. The pathway is found in the plant cytoplasm, animals, and some bacteria
(Lichtenthaler 1999; Miziorko 2011). In DOXP pathway, pyruvate and glycelaldehyde are converted to IPP. The DOXP pathway is found in cyanobacteria, the plastids
of algae and land plants, and some bacteria (Lichtenthaler 1999). Carotenoids are
synthesized in plastids. Exceptionally, among oxygenic phototrophs, the Euglenophyceae demonstrate only the MVA pathway, and the Chlorophyceae demonstrate
only the DOXP pathway (Lichtenthaler 1999; Takaichi 2011).
All carotenoids in oxygenic phototrophs consist of eight IPP units. Farnesyl
pyrophosphate (C 15 ) is synthesized from three IPPs, after which one IPP is added to
farnesyl pyrophosphate by geranylgeranyl pyrophosphate synthase (CrtE, GGPS)