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PubMed2003

Xanthophyll cycle pool size and composition in relation to the nitrogen content of apple leaves.

The objective of this study was to determine xanthophyll cycle pool size and composition in response to N status and their relationships to non-photochemical quenching in apple leaves. Bench-grafted Fuji/M.26 trees were fertilized with different N concentrations (0-20 mM) in a modified Hoagland's solution for 6 weeks to create a wide range of leaf N status (1-4.4 g m(-2)). Chlorophyll content, xanthophyll cycle pool size, lutein, total carotene, and neoxanthin on a leaf area basis all increased linearly with increasing leaf N. However, only the ratios of the xanthophyll cycle pool and of lutein to chlorophyll were higher in low N leaves than in high N leaves. Under high light at midday, both zeaxanthin (Z), expressed on a chlorophyll basis, and the percentage of the xanthophyll cycle pool present as Z, increased as leaf N decreased. Thermal dissipation of excitation energy, measured as non-photochemical quenching of chlorophyll fluorescence, was positively related to, whereas efficiency of excitation transfer and photosystem II quantum efficiency were negatively related to, Z, expressed on a chlorophyll basis or on a xanthophyll cycle pool basis. It is concluded that both xanthophyll cycle pool size (on a chlorophyll basis) and conversion of violaxanthin to zeaxanthin are enhanced in response to N limitation to dissipate excessive absorbed light under high irradiance.

Chlorophyll↗

PubMed2005

Nutritional manipulation of primate retinas, III: Effects of lutein or zeaxanthin supplementation on adipose tissue and retina of xanthophyll-free monkeys.

PURPOSE: Macular pigment (MP) is composed of the xanthophylls lutein (L) and zeaxanthin (Z) and may help to prevent age-related macular degeneration or retard its progression. In this study the effects of L or Z supplementation on carotenoid levels was examined in serum, adipose tissue, and retina in rhesus monkeys with no previous intake of xanthophylls. METHODS: From birth to 7 to 16 years of age, 18 rhesus monkeys were fed semipurified diets containing all essential nutrients but no xanthophylls. Six were supplemented with pure L and 6 with pure Z at 3.9 micromol/kg per day for 24 to 101 weeks. At baseline and at 4- to 12-week intervals, carotenoids in adipose tissue were measured by HPLC. At study completion, carotenoids in serum and retina (central 4 mm, 8-mm annulus, and the periphery) were determined. Results were compared with data from control monkeys fed a standard laboratory diet. RESULTS: Monkeys fed xanthophyll-free diets had no L or Z in serum or tissues. After L or Z supplementation, serum and adipose tissue concentrations significantly increased in the supplemented groups. Both L and 3R,3'S-Z (RSZ or meso-Z, not present in the diet) were incorporated into retinas of monkeys supplemented with L, with RSZ present only in the macula (central 4 mm). All-trans Z, but no RSZ, accumulated in retinas of monkeys supplemented with Z. CONCLUSIONS: L is the precursor of RSZ, a major component of macular pigment. Xanthophyll-free monkeys can accumulate retinal xanthophylls and provide a valuable model for examining their uptake and conversion.

Adipose Tissue↗

PubMed2004

Nutritional manipulation of primate retinas, I: effects of lutein or zeaxanthin supplements on serum and macular pigment in xanthophyll-free rhesus monkeys.

PURPOSE: The xanthophylls lutein (L) and zeaxanthin (Z) are the primary components of macular pigment (MP) and may protect the macula from age-related degeneration (AMD). In this study, L or Z was fed to rhesus monkeys reared on xanthophyll-free diets to follow the accumulation of serum carotenoids and MP over time. METHODS: Eighteen rhesus monkeys were fed xanthophyll-free semipurified diets from birth until 7 to 16 years. The diets of six were then supplemented with pure L and six with pure Z at 3.9 micromol/kg per day (2.2 mg/kg per day) for 24 to 56 weeks. At baseline and 4- to 12-week intervals during supplementation, serum carotenoids were measured by HPLC, and MP density was estimated by two-wavelength reflectometry. Serum carotenoids and MP were also measured in monkeys fed a stock diet. RESULTS: Monkeys fed xanthophyll-free diets had no L or Z in serum and no detectable MP. During supplementation, serum L or Z increased rapidly over the first 4 weeks and from 16 weeks onward maintained similar levels, both several times higher than in stock-diet-fed monkeys. The central peak of MP optical density increased to a relatively steady level by 24 to 32 weeks in both L- and Z-fed groups. Rhesus monkeys fed a stock diet had lower blood concentrations of L than those found in humans and other nonhuman primates. CONCLUSIONS: Rhesus monkeys respond to either dietary L or Z supplementation with increases in serum xanthophylls and MP, even after life-long xanthophyll deficiency. These animals provide a potential model to study mechanisms of protection from AMD.

Animals↗

PubMed2001

Ligand-binding characterization of xanthophyll carotenoids to solubilized membrane proteins derived from human retina.

The macula of the human retina contains extraordinarily high concentrations of lutein and zeaxanthin, xanthophyll carotenoids that appear to play an important role in protecting against age-related macular degeneration, the leading cause of blindness among the elderly. It is likely that the uptake and stabilization of these carotenoids is mediated by specific xanthophyll-binding proteins. In order to purify and characterize such a binding protein, a carotenoid-rich membrane fraction derived from human macula or peripheral retina was prepared by homogenization, differential centrifugation, and detergent solubilization. Further purification was carried out using ion-exchange chromatography and gel-filtration chromatography coupled with continuous photodiode-array monitoring for endogenously associated xanthophyll carotenoids. The most highly purified preparations contained two major protein bands at 25 and 55 kDa that consistently co-eluted with endogenous lutein and zeaxanthin. The visible absorbance spectrum of the binding protein preparation closely matches the spectral absorbance of the human macular pigment, and it is bathochromically shifted about 10 nm from the spectrum of lutein and zeaxanthin dissolved in organic solvents. Binding of exogenously added lutein and zeaxanthin is saturable and specific with an apparent Kd of approximately 1 microM. Canthaxanthin and beta-carotene exhibit no significant binding activity to solubilized retinal membrane proteins when assayed under identical conditions. Other potential mammalian xanthophyll-binding proteins such as albumin, tubulin, lactoglobulin and serum lipoproteins possess only weak non-specific binding affinity for carotenoids when assayed under the same stringent binding conditions. This investigation provides the first direct evidence for the existence of specific xanthophyll-binding protein(s) in the vertebrate retina and macula. The possible roles of xanthophyll-binding proteins in normal macular function and in the pathogenesis of age-related macular degeneration remain to be elucidated.

Carrier Proteins↗

PubMed1995

Xanthophyll cycle-dependent quenching of photosystem II chlorophyll a fluorescence: formation of a quenching complex with a short fluorescence lifetime.

Excess light triggers protective nonradiative dissipation of excitation energy in photosystem II through the formation of a trans-thylakoid pH gradient that in turn stimulates formation of zeaxanthin and antheraxanthin. These xanthophylls when combined with protonation of antenna pigment-protein complexes may increase nonradiative dissipation and, thus, quench chlorophyll a fluorescence. Here we measured, in parallel, the chlorophyll a fluorescence lifetime and intensity to understand the mechanism of this process. Increasing the xanthophyll concentration in the presence of a pH gradient (quenched conditions) decreases the fractional intensity of a fluorescence lifetime component centered at approximately 2 ns and increases a component at approximately 0.4 ns. Uncoupling the pH gradient (unquenched conditions) eliminates the 0.4-ns component. Changes in the xanthophyll concentration do not significantly affect the fluorescence lifetimes in either the quenched or unquenched sample conditions. However, there are differences in fluorescence lifetimes between the quenched and unquenched states that are due to pH-related, but nonxanthophyll-related, processes. Quenching of the maximal fluorescence intensity correlates with both the xanthophyll concentration and the fractional intensity of the 0.4-ns component. The unchanged fluorescence lifetimes and the proportional quenching of the maximal and dark-level fluorescence intensities indicate that the xanthophylls act on antenna, not reaction center processes. Further, the fluorescence quenching is interpreted as the combined effect of the pH gradient and xanthophyll concentration, resulting in the formation of a quenching complex with a short (approximately 0.4 ns) fluorescence lifetime.

Journal Article↗

PubMed1998

Altered xanthophyll compositions adversely affect chlorophyll accumulation and nonphotochemical quenching in Arabidopsis mutants.

Collectively, the xanthophyll class of carotenoids perform a variety of critical roles in light harvesting antenna assembly and function. The xanthophyll composition of higher plant photosystems (lutein, violaxanthin, and neoxanthin) is remarkably conserved, suggesting important functional roles for each. We have taken a molecular genetic approach in Arabidopsis toward defining the respective roles of individual xanthophylls in vivo by using a series of mutant lines that selectively eliminate and substitute a range of xanthophylls. The mutations, lut1 and lut2 (lut = lutein deficient), disrupt lutein biosynthesis. In lut2, lutein is replaced mainly by a stoichiometric increase in violaxanthin and antheraxanthin. A third mutant, aba1, accumulates normal levels of lutein and substitutes zeaxanthin for violaxanthin and neoxanthin. The lut2aba1 double mutant completely lacks lutein, violaxanthin, and neoxanthin and instead accumulates zeaxanthin. All mutants were viable in soil and had chlorophyll a/b ratios ranging from 2.9 to 3.5 and near wild-type rates of photosynthesis. However, mutants accumulating zeaxanthin exhibited a delayed greening virescent phenotype, which was most severe and often lethal when zeaxanthin was the only xanthophyll present. Chlorophyll fluorescence quenching kinetics indicated that both zeaxanthin and lutein contribute to nonphotochemical quenching; specifically, lutein contributes, directly or indirectly, to the rapid rise of nonphotochemical quenching. The results suggest that the normal complement of xanthophylls, while not essential, is required for optimal assembly and function of the light harvesting antenna in higher plants.

Arabidopsis↗

PubMed1993

The Xanthophyll Cycle, Protein Turnover, and the High Light Tolerance of Sun-Acclimated Leaves.

Changes in photosynthesis rate and photochemical characteristics in response to high irradiance, followed by recovery at low irradiance, were determined in four groups of sun-acclimated leaves of spinach (Spinacia oleracea L.). These four groups were untreated control leaves, leaves treated with either an inhibitor of energy dissipation associated with the xanthophyll cycle (dithiothreitol, DTT) or an inhibitor of chloroplast-encoded protein synthesis (chloramphenicol, CAP), as well as leaves treated with a combination of DTT + CAP. In these sun leaves, treatment with either CAP or DTT alone did not result in an inhibition of the recovery from high-light-induced decreases in photochemical efficiency. Only the treatment with a combination of CAP + DTT caused a strong and irreversible depression of photochemical efficiency. We suggest that in the presence of DTT (and in the absence of xanthophyll cycle-associated energy dissipation), protein turnover may be involved in the recovery process. We further suggest that the reversible depression of photochemical efficiency in CAP-treated sun leaves reflects xanthophyll cycle-associated energy dissipation. In the leaves treated with CAP + DTT a slowly developing decrease in the maximal yield of chlorophyll fluorescence in high light may indicate an alternative, xanthophyll cycle-independent dissipation process in the photochemical system. Moreover, CAP treatments did not cause any changes in the deepoxidation state of the xanthophyll cycle. However, CAP-treated leaves, but not those treated with CAP + DTT, exhibited some decrease in the pool size of the xanthophyll cycle during the exposure to high light.

Journal Article↗

PubMed1980

A rapid bioassay for the comparison of xanthophyll availability from various sources.

A rapid bioassay method for comparing xanthophyll availability from various sources or the pigmenting ability of genetic strains or crosses is proposed. Xanthophyll depleted, fasted birds are intubated with equal amounts of xanthophyll from various sources. Serum xanthophyll is then determined from blood samples obtained 14 to 24 hr following intubation. Results are expressed as the increase in serum xanthophyll (microgram/ml) over the intubated controls per milligram xanthophyll intubated per kilogram body weight. Limitations of the bioassay are discussed.

Animals↗

PubMed2005

Microbial xanthophylls.

Xanthophylls are oxygenated carotenoids abundant in the human food supply. Lutein, zeaxanthin, and cryptoxanthin are major xanthophyll carotenoids in human plasma. The consumption of these xanthophylls is directly associated with reduction in the risk of cancers, cardiovascular disease, age-related macular degeneration, and cataract formation. Canthaxanthin and astaxanthin also have considerable importance in aquaculture for salmonid and crustacean pigmentation, and are of commercial interest for the pharmaceutical and food industries. Chemical synthesis is a major source for the heavy demand of xanthophylls in the consumer market; however, microbial producers also have potential as commercial sources. In this review, we discuss the biosynthesis, commercial utility, and major microbial sources of xanthophylls. We also present a critical review of current research and technologies involved in promoting microbes as potential commercial sources for mass production.

Bacteria↗

PubMed2006

Distribution of macular xanthophylls between domains in a model of photoreceptor outer segment membranes.

A model of photoreceptor outer segment (POS) membranes has been proposed, consisting of an equimolar ternary mixture of 1-palmitoyl-2-docosahexaenoylphosphatidylcholine/distearoylphosphatidylcholine/cholesterol. It was shown that, as in membranes made from the raft-forming mixture, in the model of POS membranes, two domains are formed: the raft domain (detergent resistant membranes, DRM), and the bulk domain (detergent soluble membranes, DSM). Saturation-recovery EPR discrimination by oxygen transport method also demonstrated the presence of two domains in this model system in situ at a wide range of temperatures (10-55 degrees C), showing additionally that neither lutein nor zeaxanthin at 1 mol% affect the formation of these domains. These membrane domains have been separated using cold Triton X-100 extraction from a model of POS membranes containing 1 mol% of either lutein or zeaxanthin. The results indicated that the macular xanthophylls lutein and zeaxanthin are substantially excluded from DRM and remain concentrated in DSM, a domain enriched in highly unsaturated docosahexaenoyl acid which is abundant in retina membranes. The concentration of xanthophylls in DRM and DSM calculated as the mol ratio of either xanthophyll to total lipid (phospholipid+cholesterol) was 0.0028 and 0.0391, respectively. Thus, xanthophylls are about 14 times more concentrated in DSM than in DRM. No significant difference in the distribution of lutein and zeaxanthin was found. The obtained results suggest that in POS membranes macular xanthophylls should also be concentrated in domains enriched in polyunsaturated chains.

Detergents↗

PubMed2000

Organization of mixed monomolecular layers formed with the xanthophyll pigments lutein or zeaxanthin and dipalmitoylphosphatidylcholine at the argon-water interface.

Two-component monomolecular layers were formed with two xanthophyll pigments, lutein and zeaxanthin and dipalmitoylphosphatidylcholine (DPPC), at the argon-water interface. Analysis of the mean molecular area parameters versus molar fraction of the xanthophyll component shows large overadditivity (ca. 50 A2 in the case of zeaxanthin and 150 A2 in the case of lutein) in the region of low molar fractions of carotenoids (maximum at 5 mol% in the case of zeaxanthin and at 20 mol% in the case of lutein). The experimental values of a mean molecular area are in good agreement with the values expected, based on the additivity rule at high molar percentages of the xanthophylls. Absorption spectroscopy of a single monolayer at the argon-water interface in the UV-Vis region has also been applied to analyze the formation of molecular assemblies of lutein in monomolecular films. The differences in the organization of lutein-DPPC and zeaxanthin-DPPC monolayers are interpreted in terms of the aggregation of xanthophyll pigments in the layers and different orientation of both xanthophylls at the interface. The results are discussed in relation to possible physiological functions of lutein and zeaxanthin in the membranes of the retina of an eye.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2002

Analysis of xanthophylls in corn by HPLC.

An HPLC method was developed using the C-30 carotenoid column to separate and identify the major xanthophylls in corn (lutein, zeaxanthin, and beta-cryptoxanthin). A photodiode array detector and a mobile phase consisting of methyl tert-butyl ether/methanol/water was used. All three xanthophylls eluted in less than 25 min. Yellow dent corn had a total xanthophyll content of 21.97 microg/g with lutein content of 15.7 microg/g, zeaxanthin content of 5.7 microg/g, and beta-cryptoxanthin of 0.57 microg/g. Commercial corn gluten meal had a 7 times higher concentration of xanthophylls (145 microg/g), and deoiled corn contained 18 microg/g, indicating that the xanthophylls are probably bound to the zein fraction of corn proteins.

Chromatography, High Pressure Liquid↗

PubMed2000

Carotenoid binding sites in LHCIIb. Relative affinities towards major xanthophylls of higher plants.

The major light-harvesting complex of photosystem II can be reconstituted in vitro from its bacterially expressed apoprotein with chlorophylls a and b and neoxanthin, violaxanthin, lutein, or zeaxanthin as the only xanthophyll. Reconstitution of these one-carotenoid complexes requires low-stringency conditions during complex formation and isolation. Neoxanthin complexes (containing 30-50% of the all-trans isomer) disintegrate during electrophoresis, exhibit a largely reduced resistance against proteolytic attack; in addition, energy transfer from Chl b to Chl a is easily disrupted at elevated temperature. Complexes reconstituted in the presence of either zeaxanthin or lutein contain nearly two xanthophylls per 12 chlorophylls and are more resistant against trypsin. Lutein-LHCIIb also exhibits an intermediate maintenance of energy transfer at higher temperature. Violaxanthin complexes approach a xanthophyll/12 chlorophyll ratio of 3, similar to the ratio in recombinant LHCIIb containing all xanthophylls. On the other hand, violaxanthin-LHCIIb exhibits a low thermal stability like neoxanthin complexes, but an intermediate accessibility towards trypsin, similar to lutein-LHCIIb and zeaxanthin-LHCIIb. Binary competition experiments were performed with two xanthophylls at varying ratios in the reconstitution. Analysis of the xanthophyll contents in the reconstitution products yielded information about relative carotenoid affinities of three assumed binding sites. In lutein/neoxanthin competition experiments, two binding sites showed a strong preference (> 200-fold) for lutein, whereas the third binding site had a higher affinity (25-fold) to neoxanthin. Competition between lutein and violaxanthin gave a similar result, although the specificities were lower: two binding sites have a 36-fold preference for lutein and one has a fivefold preference for violaxanthin. The lowest selectivity was between lutein and zeaxanthin: two binding sites had a fivefold higher affinity for lutein and one has a threefold higher affinity to zeaxanthin.

Apoproteins↗

PubMed2002

The binding of Xanthophylls to the bulk light-harvesting complex of photosystem II of higher plants. A specific requirement for carotenoids with a 3-hydroxy-beta-end group.

The pigment composition of the light-harvesting complexes (LHCs) of higher plants is highly conserved. The bulk complex (LHCIIb) binds three xanthophyll molecules in combination with chlorophyll (Chl) a and b. The structural requirements for binding xanthophylls to LHCIIb have been examined using an in vitro reconstitution procedure. Reassembly of the monomeric recombinant LHCIIb was performed using a wide range of native and nonnative xanthophylls, and a specific requirement for the presence of a hydroxy group at C-3 on a single beta-end group was identified. The presence of additional substituents (e.g. at C-4) did not interfere with xanthophyll binding, but they could not, on their own, support reassembly. cis isomers of zeaxanthin, violaxanthin, and lutein were not bound, whereas all-trans-neoxanthin and different chiral forms of lutein and zeaxanthin were incorporated into the complex. The C-3 and C-3' diols lactucaxanthin (a carotenoid native to many plant LHCs) and eschscholtzxanthin (a retro-carotenoid) both behaved very differently from lutein and zeaxanthin in that they would not support complex reassembly when used alone. Lactucaxanthin could, however, be bound when lutein was also present, and it showed a high affinity for xanthophyll binding site N1. In the presence of lutein, lactucaxanthin was readily bound to at least one lutein-binding site, suggesting that the ability to bind to the complex and initiate protein folding may be dependent on different structural features of the carotenoid molecule. The importance of carotenoid end group structure and ring-to-chain conformation around the C-6-C-7 torsion angle of the carotenoid molecule in binding and complex reassembly is discussed.

Isomerism↗

PubMed2004

Xanthophylls and alpha-tocopherol decrease UVB-induced lipid peroxidation and stress signaling in human lens epithelial cells.

Epidemiological studies suggest that consumption of vegetables rich in the xanthophylls lutein (LUT) and zeaxanthin (ZEA) reduces the risk for developing age-related cataract, a leading cause of vision loss. Although LUT and ZEA are the only dietary carotenoids present in the lens, direct evidence for their photoprotective effect in this organ is not available. The present study examined the effects of xanthophylls and alpha-tocopherol (alpha-TC) on lipid peroxidation and the mitogen-activated stress signaling pathways in human lens epithelial (HLE) cells following ultraviolet B light (UVB) irradiation. When presented with LUT, ZEA, astaxanthin (AST), and alpha-TC as methyl-beta-cyclodextrin complexes, HLE cells accumulated the lipophiles in a concentration- and time-dependent manner with uptake of LUT exceeding that of ZEA and AST. Pretreatment of cultures with either 2 micromol/L xanthophyll or 10 micromol/L alpha-TC for 4 h before exposure to 300 J/m(2) UVB radiation decreased lipid peroxidation by 47-57% compared with UVB-treated control HLE cells. Pretreatment with the xanthophylls and alpha-TC also inhibited UVB-induced activation of c-JUN NH(2)-terminal kinase (JNK) and p38 by 50-60 and 25-32%, respectively. There was substantial inhibition of UVB-induced JNK and p38 activation for cells containing <0.20 and approximately 0.30 nmol xanthophylls/mg, respectively, whereas >2.3 nmol alpha-TC/mg protein was required to significantly decrease UVB-induced stress signaling. These data suggest that xanthophylls are more potent than alpha-TC for protecting human lens epithelial cells against UVB insult.

Epithelial Cells↗

PubMed2003

Expression of xanthophyll biosynthetic genes during light-dependent chloroplast differentiation.

In higher plants, etioplast to chloroplast differentiation is characterized by dramatic ultrastructural changes of the plastid and a concomitant increase in chlorophylls and carotenoids. Whereas the formation and function of carotenes and their oxygenated derivatives, the xanthophylls, have been well studied, little is known about the regulation of the genes involved in xanthophyll biosynthesis. Here, we analyze the expression of three xanthophyll biosynthetic genes (i.e. beta-carotene hydroxylase [bhy], zeaxanthin epoxidase [zep], and violaxanthin de-epoxidase [vde]) during de-etiolation of seedlings of tobacco (Nicotiana tabacum L. cv Samsun) under different light conditions. White-light illumination caused an increase in the amount of all corresponding mRNAs. The expression profiles of bhy and zep not only resembled each other but were also similar to the pattern of a gene encoding a major light-harvesting protein of photosystem II. This finding indicates a coordinated synthesis during formation of the antenna complex. In contrast, the expression pattern of vde was clearly different. Furthermore, the gene expression of bhy was shown to be modulated after illumination with different white-light intensities. The expression of all xanthophyll biosynthetic genes under examination was up-regulated upon exposure to red, blue, and white light. Gene expression of bhy and vde but not of zep was more pronounced under red-light illumination, pointing at an involvement of the phytochrome system. Expression analysis in the presence of the photosynthetic electron transport inhibitors 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone indicated a redox control of transcription of two of the xanthophyll biosynthetic genes (bhy and zep).

Carotenoids↗

PubMed1998

Arabidopsis mutants define a central role for the xanthophyll cycle in the regulation of photosynthetic energy conversion.

A conserved regulatory mechanism protects plants against the potentially damaging effects of excessive light. Nearly all photosynthetic eukaryotes are able to dissipate excess absorbed light energy in a process that involves xanthophyll pigments. To dissect the role of xanthophylls in photoprotective energy dissipation in vivo, we isolated Arabidopsis xanthophyll cycle mutants by screening for altered nonphotochemical quenching of chlorophyll fluorescence. The npq1 mutants are unable to convert violaxanthin to zeaxanthin in excessive light, whereas the npq2 mutants accumulate zeaxanthin constitutively. The npq2 mutants are new alleles of aba1, the zeaxanthin epoxidase gene. The high levels of zeaxanthin in npq2 affected the kinetics of induction and relaxation but not the extent of nonphotochemical quenching. Genetic mapping, DNA sequencing, and complementation of npq1 demonstrated that this mutation affects the structural gene encoding violaxanthin deepoxidase. The npq1 mutant exhibited greatly reduced nonphotochemical quenching, demonstrating that violaxanthin deepoxidation is required for the bulk of rapidly reversible nonphotochemical quenching in Arabidopsis. Altered regulation of photosynthetic energy conversion in npq1 was associated with increased sensitivity to photoinhibition. These results, in conjunction with the analysis of npq mutants of Chlamydomonas, suggest that the role of the xanthophyll cycle in nonphotochemical quenching has been conserved, although different photosynthetic eukaryotes rely on the xanthophyll cycle to different extents for the dissipation of excess absorbed light energy.

Amino Acid Sequence↗

PubMed1992

Antioxidant activity of xanthophylls on peroxyl radical-mediated phospholipid peroxidation.

The ability of xanthophylls (canthaxanthin, zeaxanthin, and astaxanthin) as chain-breaking antioxidants was investigated in peroxyl radical-mediated peroxidation of phosphatidylcholine (PC) liposomes under atmospheric conditions using lipid-soluble and water-soluble radical generators. These xanthophylls retarded the chain propagation reaction of phosphatidylcholine hydroperoxides (PC-OOH) formation, although their activities to trap chain-carrying peroxyl radical were much less than that of alpha-tocopherol. In chick plasma studies, it was observed that endogenious xanthophylls participated in the antioxidant defenses against the attack of aqueous peroxyl radical. It was concluded that xanthophylls possess the ability to act as chain-breaking antioxidants in the peroxidation of membraneous phospholipids. Dietary xanthophylls may, therefore, be helpful in resisting membraneous phospholipids against oxidative damage in vivo.

Animals↗