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Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. 
The name is from Greek xanthos (ξανθός, "yellow") and phyllon (φύλλον, "leaf"), due to their formation of the yellow band seen in early chromatography of leaf pigments.

Molecular structure
As both are carotenoids, xanthophylls and carotenes are similar in structure, but xanthophylls contain oxygen atoms while carotenes are purely hydrocarbons, which do not contain oxygen. 
Their content of oxygen causes xanthophylls to be more polar (in molecular structure) than carotenes, and causes their separation from carotenes in many types of chromatography. (Carotenes are usually more orange in color than xanthophylls.) 
Xanthophylls present their oxygen either as hydroxyl groups and/or as hydrogen atoms substituted by oxygen atoms when acting as a bridge to form epoxides.

Like other carotenoids, xanthophylls are found in highest quantity in the leaves of most green plants, where they act to modulate light energy and perhaps serve as a non-photochemical quenching agent to deal with triplet chlorophyll (an excited form of chlorophyll), which is overproduced at high light levels in photosynthesis. 
The xanthophylls found in the bodies of animals including humans, and in dietary animal products, are ultimately derived from plant sources in the diet. 
For example, the yellow color of chicken egg yolks, fat, and skin comes from ingested xanthophylls—primarily lutein, which is added to chicken feed for this purpose.

The yellow color of the macula lutea (literally, yellow spot) in the retina of the human eye results from the presence of lutein and zeaxanthin. 
Again, both these specific xanthophylls require a source in the human diet to be present in the human eye. 
They protect the eye from ionizing light (blue and ultraviolet light), which they absorb; but xanthophylls do not function in the mechanism of sight itself as they cannot be converted to retinal (also called retinaldehyde or vitamin A aldehyde).
Their physical arrangement in the macula lutea is believed to be the cause of Haidinger's brush, an entoptic phenomenon that enables perception of polarizing light.

Example compounds
The group of xanthophylls includes (among many other compounds) lutein, zeaxanthin, neoxanthin, violaxanthin, flavoxanthin, and α- and β-cryptoxanthin. 
The latter compound is the only known xanthophyll to contain a beta-ionone ring, and thus β-cryptoxanthin is the only xanthophyll that is known to possess pro-vitamin A activity for mammals. 
Even then, it is a vitamin only for plant-eating mammals that possess the enzyme to make retinal from carotenoids that contain beta-ionone (some carnivores lack this enzyme). 
In species other than mammals, certain xanthophylls may be converted to hydroxylated retinal-analogues that function directly in vision. 
For example, with the exception of certain flies, most insects use the xanthophyll derived R-isomer of 3-hydroxyretinal for visual activities, which means that β-cryptoxanthin and other xanthophylls (such as lutein and zeaxanthin) may function as forms of visual "vitamin A" for them, while carotenes (such as beta carotene) do not.

Xanthophyll cycle
The xanthophyll cycle involves the enzymatic removal of epoxy groups from xanthophylls (e.g. violaxanthin, antheraxanthin, diadinoxanthin) to create so-called de-epoxidised xanthophylls (e.g. diatoxanthin, zeaxanthin). 
These enzymatic cycles were found to play a key role in stimulating energy dissipation within light-harvesting antenna proteins by non-photochemical quenching- a mechanism to reduce the amount of energy that reaches the photosynthetic reaction centers. 
Non-photochemical quenching is one of the main ways of protecting against photoinhibition.
In higher plants, there are three carotenoid pigments that are active in the xanthophyll cycle: violaxanthin, antheraxanthin, and zeaxanthin. 
During light stress, violaxanthin is converted to zeaxanthin via the intermediate antheraxanthin, which plays a direct photoprotective role acting as a lipid-protective anti-oxidant and by stimulating non-photochemical quenching within light-harvesting proteins. 
This conversion of violaxanthin to zeaxanthin is done by the enzyme violaxanthin de-epoxidase, while the reverse reaction is performed by zeaxanthin epoxidase.

In diatoms and dinoflagellates, the xanthophyll cycle consists of the pigment diadinoxanthin, which is transformed into diatoxanthin (diatoms) or dinoxanthin (dinoflagellates) under high-light conditions.
found that, "The increase in zeaxanthin appears to surpass the decrease in violaxanthin in spinach" and commented that the discrepancy could be explained by "a synthesis of zeaxanthin from beta-carotene", however they noted further study is required to explore this hypothesis.

Food sources
Xanthophylls are found in all young leaves and in etiolated leaves. Examples of other rich sources include papaya, peaches, prunes, and squash, which contain lutein diesters.
Kale contains about 18mg lutein and zeaxanthin per 100g, spinach about 11mg/100g, parsley about 6mg/100g, peas about 3mg/110g, squash about 2mg/100g, and pistachios about 1mg/100g.

The chlorophylls (and there are several different types) are the main light absorbing pigments in land plants.  
They are located in the chloroplasts of the palisade and spongy mesophyll layers of the leaves.  
The chlorophylls mainly absorb red and blue wavelengths  of light.   
Apart from the chlorophylls, plants have other pigments - often termed the accessory pigments - notably the carotenes and the xanthophylls.

Carotenes are hydrocarbons - made up of carbon and hydrogen and they contribute to photosynthesis by transmitting the light energy they absorb to chlorophyll. 
They also protect plant tissues by helping to absorb energy from an ‘excited form’ of the oxygen molecule [O2 ], which is formed during photosynthesis.

The carotenes are also responsible for the orange (but not all of the yellow) colours in autumnal leaves and dry foliage; and for the colours of many other fruits, vegetables and fungi (for example, cantaloupe melon, sweet potatoes,  and chanterelle).

The xanthophylls are yellow pigments. Their molecular structure is similar to that of the carotenes.   Xanthophylls have some oxygen as well in their structure. 
The xanthophylls, e.g. violaxanthin and zeaxanthin, can pass this light energy between themselves and convert some of this light energy into heat energy.
This can be used to prevent damage to the light harvesting complexes in the chloroplasts. 
This process is known as the xanthophyll cycle.  

Evergreen conifers, like pine and spruce, face a problem in winter - they have leaves.
But it is too cold to fix carbon through photosynthesis, but their chlorophyll molecules are still absorbing light energy.  
Xanthophylls is vital that they have a mechanism to dissipate this absorbed light.   
This is where the accessory photosynthetic pigments - the xanthophylls are important.  
The operation of the xanthophyll cycle allows the plants to cope with the absorbed light in the winter months, protecting the light absorbing complexes and allowing the plants to recover from the winter conditions and begin the process of photosynthesis, as and when the temperatures allow.

Xanthophyll is a type of accessory pigment or phytochemicals, which belongs to the class of “Carotenoids”. 
In many vascular plants and algae, xanthophylls act as the light-harvesting protein complexes. Xanthophylls are rich in antioxidants, which prevent the cells from damaging. 
In photosynthetic eukaryotes, the xanthophylls are usually bound to the chlorophyll molecules.

Xanthophylls are the pigment molecules present within the light-harvesting complex, which protect the photosynthetic organisms from the toxic effect of light. 
In this context, you will get to know the meaning, molecular structure, occurrence, types, cycle, functions and isolation of xanthophyll.

Meaning of Xanthophyll
Xanthophyll merely refers to the light-harvesting accessory pigments, which work coordinately with the chlorophyll-a. 
Xanthophylls can absorb light of a wavelength in a range of 425-475 nm. 
Xanthophylls are primarily of three types, namely lutein, zeaxanthin and cryptoxanthin. 
They are highly antioxygenic molecules, which protect the cell from damage and ageing.

Xanthophyll is highly beneficial for eye health, as it reduces the risk of eye cataract and macular degeneration. 
Xanthophylls or Phylloxanthins are the yellow colour pigment naturally present in the plants.
A xanthophyll can isolate from the plant extract.

You can isolate the xanthophyll pigment from the plant extract by performing chromatography, which results in the formation of a yellow colour band over a chromatography paper. 
Let us look into some of the general properties of the xanthophyll.

Molecular Structure
Xanthophyll is the primary accessory pigment. 
Xanthophylls consists of  C-40 terpenoid compounds, which forms as a result of condensation between the isoprene units. 
The molecular structure of xanthophyll and carotene (another accessory pigment) is almost the same except for the presence of an oxygen atom. In xanthophyll, there is an oxygen atom present as the hydroxyl group, whereas carotene lacks an oxygen atom and exists as a pure hydrocarbon.

Xanthophylls occur naturally in the plants, which regulate the light energy and act as “Photochemical quenching agent” that deals with the exciting form of chlorophyll or triplet chlorophyll. 
The triplet chlorophyll produces at a higher rate during the photosynthetic process.
Xanthophylls are also found in the body of humans and animals, which comes ultimately by the source of green plants.

Xanthophylls (originally phylloxanthins) are yellow pigments from the carotenoid group. 
Their molecular structure is based on carotenes; contrary to the carotenes, some hydrogen atoms are substituted by hydroxyl groups and/or some pairs of hydrogen atoms are substituted by oxygen atoms. 
They are found in the leaves of most plants and are synthesized within the plastids. 
They are involved in photosynthesis along with green chlorophyll, which typically covers up the yellow except in autumn, when the chlorophyll is denatured by the cold.

In plants, xanthophylls are considered accessory pigments, along with anthocyanins, carotenes, and sometimes phycobiliproteins. 
Xanthophylls, along with carotenic pigments are seen when leaves turn orange in the autumn season.

Animals cannot produce xanthophylls, and thus xanthophylls found in animals (e.g. in the eye) come from their food intake. 
The yellow color of chicken egg yolks also comes from ingested xanthophylls.

Xanthophylls are oxidized derivatives of carotenes. 
They contain hydroxyl groups and are more polar; therefore, they are the pigments that will travel the furthest in paper chromatography.

The group of xanthophylls is composed of lutein, zeaxanthin, and α- and β-cryptoxanthin.

Xanthophyll has a chemical formula of C40H56O2.

Xanthophyll cycle
The xanthophyll cycle involves conversions of pigments from a non-energy-quenching form to energy-quenching forms. 
This is a way to reduce the absorption cross-section of the light harvesting antenna, and thus to reduce the amount of energy that reaches the photosynthetic reaction centers. 
Reducing the light harvesting antenna is one of the main ways of protecting against photoinhibition and changes in the xanthophyll cycling takes place on a time scale of minutes to hours. 
In higher plants there are three carotenoid pigments that are active in the xanthophyll cycle: violaxanthin, antheraxanthin and zeaxanthin.
During light stress violoxanthin is converted to antheraxanthin and zeaxanthin, which functions as photoprotective pigments. 
This conversion is done by the enzyme violaxanthin de-epoxidase.

In diatoms and dinoflagellates the xanthophyll cycle consists of the pigment diadinoxanthin, which is transformed into diatoxanthin (diatoms) or dinoxanthin (dinoflagellates), at high light.

Photosynthesis is the conversion of light energy into chemical energy utilized by plants, many algae, and cyanobacteria. However, each photosynthetic organism must be able to dissipate the light radiation that exceeds its capacity for carbon dioxide fixation before it can damage the photosynthetic apparatus (i.e., the chloroplast ). 
This photoprotection is usually mediated by oxygenated carotenoids, i.e., a group of yellow pigments termed xanthophylls, including violaxanthin, antheraxanthin, and zeaxanthin, which dissipate the thermal radiation from the sunlight through the xanthophyll cycle.

Xanthophylls are present in two large protein-cofactor complexes, present in photosynthetic membranes of organisms using Photosystem I or Photosystem II. 
Photosystem II uses water as electron donors, and pigments and quinones as electron acceptors, whereas the Photosystem I uses plastocyanin as electron donors and iron-sulphur centers as electron acceptors. 
Photosystem I in thermophilic Cyanobacteria, for instance, is a crystal structure that contains 12 protein subunits, 2 phylloquinones, 22 carotenoids, 127 cofactors constituting 96 chlorophylls, besides calcium cations, phospholipids, three iron-sulphur groups, water, and other elements. 
This apparatus captures light and transfers electrons to pigments and at the same time dissipates the excessive excitation energy via the xanthophylls.

Xanthophylls are synthesized inside the plastids and do not depend on light for their synthesis as do chlorophylls. 
From dawn to sunset, plants and other photosynthetic organisms are exposed to different amounts of solar radiation, which determine the xanthophyll cycle. 
At dawn, a pool of diepoxides termed violaxanthin is found in the plastids, which will be converted by the monoepoxide antheraxanthin into zeaxanthin as the light intensity gradually increases during the day. 
Zeaxanthin absorbs and dissipates the excessive solar radiation that is not used by chlorophyll during carbon dioxide fixation. 
At the peak hours of sunlight exposition, almost all xanthophyll in the pool is found under the form of zeaxanthin, which will be gradually reconverted into violaxanthin as the solar radiation decreases in the afternoon to be reused again in the next day.

General description
Xanthophylls are oxygenated derivatives of carotenoids. 
Xanthophylls consists of oxygen atoms. 
Xanthophylls are yellow pigments and are found majorly in the leaves of most green plants.

Xanthophyll has been used:
to quantify circulating lutein in birds
to study its effect on the synthesis of factor D (FD) by adipocytes
for the quantification of carotenoids from the leaves of Brassica oleracea

Biochem/physiol Actions
Xanthophyll/Lutein functions as an accessory light-harvesting pigment. 
Xanthophylls also acts as quenchers of singlet oxygen and chlorophyll triplet states to exhibit protection against photooxidative damage. 
Xanthophyll is involved in photosynthesis. 
Xanthophylls has antioxidant properties.
Dietary carotenoid with no vitamin A potency. 
Increases macular pigment concentration in the eye and may improve visual function.

Xanthophylls are oxygenated carotenoids playing an essential role as structural components of the photosynthetic apparatus. 
Xanthophylls contribute to the assembly and stability of light-harvesting complex, to light absorbance and to photoprotection. 
The first step in xanthophyll biosynthesis from α- and β-carotene is the hydroxylation of e- and β-rings, performed by both non-heme iron oxygenases (CHY1, CHY2) and P450 cytochromes (LUT1/CYP97C1, LUT5/CYP97A3). 
The Arabidopsis triple chy1chy2lut5 mutant is almost completely depleted in β-Xanthophylls. 
Here we report on the quadruple chy1chy2lut2lut5 mutant, additionally carrying the lut2 mutation (affecting lycopene e-cyclase). 
This genotype lacks lutein and yet it shows a compensatory increase in β-Xanthophylls with respect to chy1chy2lut5 mutant.
Mutant plants show an even stronger photosensitivity than chy1chy2lut5, a complete lack of qE, the rapidly reversible component of non-photochemical quenching, and a peculiar organization of the pigment binding complexes into thylakoids. 
Biochemical analysis reveals that the chy1chy2lut2lut5 mutant is depleted in Lhcb subunits and is specifically affected in Photosystem I function, showing a deficiency in PSI-LHCI supercomplexes. 
Moreover, by analyzing a series of single, double, triple and quadruple Arabidopsis mutants in xanthophyll biosynthesis, we show a hitherto undescribed correlation between xanthophyll levels and the PSI-PSII ratio. 
The decrease in the xanthophyll/carotenoid ratio causes a proportional decrease in the LHCII and PSI core levels with respect to PSII. 
The physiological and biochemical phenotype of the chy1chy2lut2lut5 mutant shows that (i) LUT1/CYP97C1 protein reveals a major β-carotene hydroxylase activity in vivo when depleted in its preferred substrate α-carotene; (ii) Xanthophylls are needed for normal level of Photosystem I and LHCII accumulation.

Xanthophylls are oxygenated carotenoids that serve a variety of functions in photosynthetic organisms and are essential for survival of the organism. 
Within the last decade, major nor advances have been made in the elucidation of the molecular genetics and biochemistry of the xanthophyll biosynthesis pathway. 
Microalgae, yeast, or other microorganisms produce some of the xanthophylls that are being commercially used due to their own color and antioxidant properties. 
Currently, only a few microalgae are being considered or already being exploitd for the production of high-value xanthophylls. 
However, new developments in molecular biology have important implications for the commercialization of microalgae, and make the genetic manipulation of the xanthophyll content of microalgae mure attractive for biotechnological purposes. 
Accordingly, the current review summarizes the general properties of xanthophylls in microalgae and the recent developments in the biotechnological production of xanthophylls.

Xanthophylls are planted in the loftiest volume in the leaves of utmost green plants and help in photosynthesis by landing light. 
Xanthophylls plant in the bodies of numerous creatures including humans, and salutary beast products, are eventually deduced from factory sources in the diet. 
The amount of oxygen causes xanthophylls to be more polar (in molecular structure) as compared to carotenes, which causes their separation from carotenes in numerous types of chromatography. 

What are Xanthophylls?
Xanthophylls refer to the light-harvesting accessory colors, which work coordinately with chlorophyll-a. Xanthophylls can absorb light of a wavelength in a range of 425-475 nm. 
Xanthophylls are primarily of three types, videlicet lutein, zeaxanthin, and cryptoxanthin. 
They're largely antioxygenic motes, which cover the cell from damage and aging.

Xanthophylls reduce the threat of eye cataracts and macular degeneration. 
Xanthophylls or Phylloxanthins are the unheroic color naturally present in the plants. 
A xanthophyll can be insulated from the factory excerpt.

Xanthophyll is the primary accessory color. 
Xanthophylls consists of C-40 terpenoid composites, which form as a result of condensation between the isoprene units. 
The molecular structure of xanthophyll and carotene (another accessory color) is nearly the same except for the presence of an oxygen snippet. 
In xanthophyll, there's an oxygen snippet present as the hydroxyl group, whereas carotene lacks an oxygen snippet and exists as a pure hydrocarbon.

Types of Xanthophylls
Xanthophylls substantially include appurtenant colors like Lutein, Zeaxanthin, and Cryptoxanthin.

Lutein is the most common xanthophyll, which is synthesized by the green plants themselves. Spinach, kale, kiwi, green apples, egg thralldom, sludge, etc. are the sources of lutein. 
Lutein is a lipophilic patch ( undoable in polar detergent-like water). 
In plants, lutein is present as adipose acid esters, in which one or two adipose acids attach with the two – OH groups.
Lutein substantially absorbs blue light, and thereby it protects the eye from the blue light that leads to an eye impairment.

Zeaxanthin simply refers to carotenoid alcohols, which can be synthesized naturally by plants and certain microorganisms. 
Xanthophylls acts as a non-photochemical quenching agent. 
Zeaxanthin is an appurtenant color, which gives distinct color to the sludge, wolfberries, etc. 
Xanthophylls consists of two chiral centers. 
Kale, spinach, turnip flora, mustard flora, etc. are the sources.

Cryptoxanthin Its molecular structure is relatively analogous to the β-carotene, but a hydroxyl group is present in addition. 
Cryptoxanthin is a plant as red crystalline solid in its pure form. 
Xanthophylls also refers to provitamin-A, as during the xanthophyll cycle, cryptoxanthin converts into vitamin A (retinol).

Xanthophyll Cycle
The xanthophyll cycle occurs inside the thylakoid membrane of the chloroplast. 
The Xanthophyll cycle facilitates the interconversion of oxygenated carotenoids. 
There are numerous types of xanthophyll cycle, but the violaxanthin and Diadinoxanthin cycles are the most common.

The main difference between carotene and xanthophyll is that carotene gives an orange color whereas xanthophyll gives a yellow color. 
Furthermore, carotene is a hydrocarbon that does not contain an oxygen atom in its structure while xanthophyll is a hydrocarbon that contains an oxygen atom in its structure.

Carotene and xanthophyll are the two classes of carotenoids, which are tetraterpene plant pigments, serving as accessory pigments in photosynthesis. 
They are responsible for giving red-orange to yellow color, especially to fruits and vegetables.

Xanthophyll is the second type of carotenoids found in plants, giving a yellow color to the plant. 
However, the structure of xanthophyll contains a single oxygen atom in contrast to carotene. 
However, same as carotene, xanthophyll occurs in leaves of plants in high quantities. 
In addition, animal bodies contain xanthophyll, which is plant-based. 
As examples, the egg yolk, fat tissue, and the skin contain xanthophyll derived from plants. 
Primarily, lutein is the form of xanthophylls found in the egg yolk of chickens. 

Also, two types of xanthophylls known as lutein and zeaxanthin occur in the macula lutea or the yellow spot in the retina of the human eye. 
They are responsible for the central vision of the eye. Moreover, they protect the eye from the blue light. 
Therefore, kale, spinach, turnip greens, summer squash, pumpkin, paprika, yellow-fleshed fruits, avocado, and egg yolk are good sources of lutein and zeaxanthin. 
In general, these two xanthophylls are effective in age-related macular degeneration (AMD), which leads to blindness. 
Furthermore, lutein is known to prevent the atherosclerosis formation due to its antioxidant effect on cholesterol, which in turn prevents the building up of cholesterol in arteries.

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