Neoxanthin

CRTR-e = e-ring hydroxyiase CRTR-b = p-ring hydroxylase ZEP-1 = zeaxanthin epoxidase NXS = neoxanthin synthase VDE 1 = violaxanthin de-epoxidase. 

P = phytoene PF = phytofluene -C = -carotene L = lycopene y-C = y-carotene p-C = p-carotene Lut = lutein Viola = violaxanthin Neo = neoxanthin d.p.b. days post breaker. 

BOUVIER F, d harlingue A, BACKHAUs R A, KUMAGAi H and CAMARA B (2000) Identification of neoxanthin synthase as a carotenoid cyclase pmalog , FEBSLetters, 267, 6346-52. BRAMLEY P M (1993) Inhibition of carotenoid biosynthesis , in Yoimg A J and Britton G, Carotenoids in Photosynthesis, London, Chapman and HaU, 127-59. 

Most of this amount is in the form of fucoxanthin in various algae and in the three main carotenoids of green leaves lutein, violaxanthin, and neoxanthin. Others produced in much smaller amounts but found widely are p-carotene and zeaxanthin. The other pigments found in certain plants are lycopene and capsanthin (Figure 2.2.1). Colorant preparations have been made from all of these compounds and obviously the composition of a colorant extract reflects the profile of the starting material. Carotenoids are probably the best known of the food colorants derived from natural sources. ... 

Typically several different carotenoids occur in plant tissues containing this class of pigments. Carotenoids are accumulated in chloroplasts of all green plants as mixtures of a- and P-carotene, P-cryptoxanthin, lutein, zeaxanthin, violaxanthin, and neoxanthin. These pigments are found as complexes formed by noncovalent bonding with proteins. In green leaves, carotenoids are free, nonesterified, and their compositions depend on the plant and developmental conditions. In reproductive... 

Physiologically, violaxanthin is an important component of the xanthophyU cycle a high light stress-induced de-epoxidation of the violaxanthin pool to the more photoprotective zeaxanthin is mediated by violaxanthin de-epoxidase (VDE). Violaxanthin and neoxanthin, an enzymatically (NXS)-produced structural isomer, are the precursors for the abscisic acid (ABA) biosynthetic pathway (Figure 5.3.1, Pathway 4 and Figure 5.3.2). In non-photosynthetic tissues, namely ripe bell peppers, antheraxanthin and violaxanthin are precursors to the red pigments, capsanthin and capsorubin, respectively (Figure 5.3.3B). 

Dunaliella natural P-carotene is distributed widely in many different markets under three categories p-carotene extracts, Dunaliella powder for human use, dried Dunaliella for feed use. Extracted purified P-carotene is sold mostly in vegetable oil in bulk concentrations from 1 to 20% to color various food products and for personal use in soft gels usually containing 5 mg P-carotene per gel. Purified natural p-carotene is generally accompanied by the other Dunaliella carotenoids, primarily lutein, neoxanthin, zeaxan-thin, violaxanthin, cryptoxanthin, and a-carotene for a total of approximately 15% of carotene concentration. This compound is marketed as carotenoids mix. ... 

Neochrome + neoxanthin, violaxanthin, luteoxanthin, lutein, zeaxanthin, 5,6,5,6-diepoxy-P-cryptoxanthin, 5,6-epoxy-P-cryptoxanthin, 5,8-epoxy-P-cryptoxanthin, zeinoxanthin, P-cryptoxanthin, 5,6,5,6-diepoxy-P-carotene, 5,8-epoxy-P-carotene, a-carotene, P-carotene... 

Neoxanthin, neoxanthin isomer, neochrome, neochrome 18 Acerola ... 

Neoxanthin, violaxanthin, zeaxanthin, lutein, antheraxanthin, P-cryptoxanthin, lutein monoester, antheraxanthin monoester, P-cryptoxanthin monoester, lycopene, P-carotene, violaxanthin ester, lutein diester, P-cryptoxanthin ester, P-cryptoxanthin ester, zeaxanthin diester, zeaxanthin diester, zeaxanthin diester... 

Allenic groups — Neoxanthin, a xanthophyll found in many foods, has an allenic group at the C-6,7,8 position where the two double bonds are perpendicular to each other, and the C-7,8 double bond coplanar with the polyene chain contributing effectively to the chromophore since the C-6,7 bond is in a different plane, it makes no contribution. Therefore, neoxanthin, despite its 10 conjugated double bonds, has a UV-Vis spectrum similar to that of a conjugated nonaene such as violaxanthin. 

Carotenoids are present at low levels in tea leaf.60 Neoxanthin, violaxanthin, lutein, and B-carotene are the major components of this group. They enter into reactions that lead to aroma formation.61... 

Neoxanthin Distortion upon Aggregation and Crystallization of LHCII... 

Fucoxanthin, lutein, neoxanthin, violaxanthin, and zeaxanthin are the most common xanthophylls on our planet. They are found in the photosynthetic machinery of algae (fucoxanthin) and higher plants (Figure 7.1). Interestingly, lutein and zeaxanthin have also been found in the retina of humans and some primates (Khachik et al., 1997 Landrum and Bone, 2001). It is likely that these carotenoids possess some universal photophysical properties essential for both photosynthesis and vision (Britton, 1995). 

The structure of the major trimeric LHCII complex has been recently obtained at 2.72 A (Figure 7.3) (Liu et al., 2004). It was revealed that each 25kDa protein monomer contains three transmembrane and three amphiphilic a-helixes. In addition, each monomer binds 14 chlorophyll (8 Chi a and 6 Chi b) and 4 xanthophyll molecules 1 neoxanthin, 2 luteins, and 1 violaxanthin. The first three xanthophylls are situated close to the integral helixes and are tightly bound to some amino acids by hydrogen bonds to hydroxyl oxygen atoms and van der Waals interactions to chlorophylls, and hydrophobic amino acids such as tryptophan and phenylalanine. 

FIGURE 7.4 Absorption (a) and resonance Raman (b) spectra of the four major xanthophylls of I.HCII antenna zeaxanthin (Zea), lutein (Lut), violaxanthin (Vio), and neoxanthin (Neo). 

Resonance Raman spectra of all four LHCII xanthophylls reveal differences in the v, frequencies, which normally depends upon the conjugation number (Heyde et al 1971 Rimai et al 1973). In addition, the neoxanthin transition is further upshifted reflecting the m-conformation. The v, region of this xanthophyll possesses additional bands at 1120,1132, and 1203 cm-1 characteristic for the 9-cis configuration (Hu et al., 1997). The v3 band frequency also differs in these xanthophylls. Finally, v4 is small and featureless in all isolated pigments. 

Neoxanthin and the two lutein molecules have close associations with three transmembrane helixes, A, B, and C, forming three chlorophyll-xanthophyll-protein domains (Figure 7.5). Considering the structure of LHCII complex in terms of domains is useful for understanding how the antenna system works, and the functions of the different xanthophylls. Biochemical evidence suggests that these xanthophylls have a much stronger affinity of binding to LHCII in comparison to violaxanthin... 

FIGURE 7.5 Structural domains of LHCII xanthophylls. Aromatic amino acids tyrosine in the neoxanthin domain and tryptophan and phenylalanine in the violaxanthin domain are labeled as Y, W, and F, respectively. 

Identification of Neoxanthin The 9-cis Requirement for a Xanthophyll in the C-Helix Domain... 

---