Introduction

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 and phyllon due to their formation of the yellow band seen in early chromatography of leaf pigments.

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.

Xanthophyll pigment

Xanthophyll pigments have critical structural and functional roles in the photosynthetic light-harvesting complexes of algae and vascular plants. Genetic dissection of xanthophyll metabolism in the green alga Chlamydomonas reinhardtii revealed functions for specific xanthophylls in the nonradiative dissipation of excess absorbed light energy, measured as nonphotochemical quenching of chlorophyll fluorescence. Mutants with a defect in either the α- or β-branch of carotenoid biosynthesis exhibited less nonphotochemical quenching but were still able to tolerate high light.

In contrast, a double mutant that was defective in the synthesis of lutein, loroxanthin (α-carotene branch), zeaxanthin, and antheraxanthin (β-carotene branch) had almost no nonphotochemical quenching and was extremely sensitive to high light. These results strongly suggest that in addition to the xanthophyll cycle pigments (zeaxanthin and antheraxanthin), α-carotene-derived xanthophylls such as lutein, which are structural components of the subunits of the light-harvesting complexes, contribute to the dissipation of excess absorbed light energy and the protection of plants from photo-oxidative damage.

The xanthophylls comprise a diverse group of oxygenated carotenoids with varied structures and multiple functions (1). In almost all photosynthetic eukaryotes, the majority of xanthophylls are bound with chlorophyll (Chl) molecules to proteins of integral membrane, light-harvesting complexes (LHCs) (2–5). The LHCs absorb and transfer excitation energy to the photosynthetic reaction centers to drive electron transport; these reactions convert light energy into chemical energy that is used to fix atmospheric CO2 into sugars. Xanthophylls can function as accessory light-harvesting pigments, as structural entities within the LHC, and as molecules required for the protection of photosynthetic organisms from the potentially toxic effects of light.

Xanthophylls have properties similar to lipids, being insoluble in water, and thus share similar transport mechanisms in the aqueous environment of the body. Many factors affect their bioavailability from the diet, including processing, meal composition and digestive enzyme activity (2). In the digestive tract, xanthophylls are incorporated into micelles and cross the enterocyte by simple passive diffusion or via several proposed lipid transporters. β-Cryptoxanthin, the only provitamin A xanthophyll, is partially cleaved to vitamin A by β-carotene-15,15′-oxygenase, while the other xanthophylls are incorporated into chylomicrons and secreted from the lymph into the blood.

The journal invites different types of articles including original research article, review articles, short note communications, case reports, Editorials, letters to the Editors and expert opinions & commentaries from different regions for publication. A standard editorial manager system is utilized for manuscript submission, review, editorial processing and tracking which can be securely accessed by the authors, reviewers and editors for monitoring and tracking the article processing.

Manuscripts can be uploaded directly through mail id: ophthalmologist@eclinicalsci.com 

Online Submission: https://www.pulsus.com/submissions/ophthalmologist-clinical-therapeutic-journal.html

Media Contact
Sarah Rose
Journal Manager
The Ophthalmologist: Clinical and Therapeutic Journal
Email: ophthalmologist@eclinicalsci.com