Editing Fucoxanthin (section)

== Function ==
[[Carotenoid]]s are pigments produced by plants and algae and play a role in light harvesting as part of the [[photosynthesis]] process. Xanthophylls are a subset of carotenoids, identified by the fact that they are oxygenated either as hydroxyl groups or as epoxide bridges. This makes them more water soluble than carotenes such as beta-carotene. Fucoxanthin is a xanthophyll that contributes more than 10% of the estimated total production of carotenoids in nature.<ref>{{cite journal | vauthors = Dembitsky VM, Maoka T | title = Allenic and cumulenic lipids | journal = Progress in Lipid Research | volume = 46 | issue = 6 | pages = 328–75 | date = November 2007 | pmid = 17765976 | doi = 10.1016/j.plipres.2007.07.001 }}</ref> It is an accessory pigment found in the chloroplasts of many [[brown macroalgae]], such as ''[[Fucus]]'' {{abbr|spp.|species}}, and the golden-brown unicellular microalgae, the [[diatom]]s. It absorbs blue and green light at bandwidth 450–540&nbsp;nm, imparting a brownish-olive color to algae.
Fucoxanthin has a highly unique structure that contains both an epoxide bond and hydroxyl groups along with an [[allenes|allenic]] bond (two adjacent carbon-carbon double bonds) and a conjugated carbonyl group (carbon-oxygen double bond) in the polyene chain. All of these features provide fucoxanthin with powerful antioxidant activity.<ref>{{cite journal | vauthors = Hu T, Liu D, Chen Y, Wu J, Wang S | title = Antioxidant activity of sulfated polysaccharide fractions extracted from Undaria pinnitafida in vitro | journal = International Journal of Biological Macromolecules | volume = 46 | issue = 2 | pages = 193–8 | date = March 2010 | pmid = 20025899 | doi = 10.1016/j.ijbiomac.2009.12.004 }}</ref>

In macroalgal plastids, fucoxanthin acts like an [[antenna pigment|antenna]] for light harvesting and energy transfer in the photosystem [[light harvesting complex]]es.<ref>{{cite journal | vauthors = Owens TG, Wold ER | title = Light-Harvesting Function in the Diatom Phaeodactylum tricornutum: I. Isolation and Characterization of Pigment-Protein Complexes | journal = Plant Physiology | volume = 80 | issue = 3 | pages = 732–8 | date = March 1986 | pmid = 16664694 | pmc = 1075192 | doi=10.1104/pp.80.3.732}}</ref> In diatoms like ''[[Phaeodactylum tricornutum]]'', fucoxanthin is protein-bound along with chlorophyll to form a light harvesting protein complex.<ref>{{cite journal | vauthors = Guglielmi G, Lavaud J, Rousseau B, Etienne AL, Houmard J, Ruban AV | title = The light-harvesting antenna of the diatom Phaeodactylum tricornutum. Evidence for a diadinoxanthin-binding subcomplex | journal = The FEBS Journal | volume = 272 | issue = 17 | pages = 4339–48 | date = September 2005 | pmid = 16128804 | doi = 10.1111/j.1742-4658.2005.04846.x | url = https://hal.archives-ouvertes.fr/hal-01094626/file/Guglielmi_FEBS-J_Modif.pdf | doi-access = free }}</ref> Fucoxanthin is the dominant carotenoid, responsible for up to 60% of the energy transfer to [[chlorophyll a]] in diatoms.<ref>{{cite journal | vauthors = Papagiannakis E, van Stokkum IH, Fey H, Büchel C, van Grondelle R | title = Spectroscopic characterization of the excitation energy transfer in the fucoxanthin-chlorophyll protein of diatoms | journal = Photosynthesis Research | volume = 86 | issue = 1–2 | pages = 241–50 | date = November 2005 | pmid = 16172942 | doi = 10.1007/s11120-005-1003-8 }}</ref> When bound to protein, the absorption spectrum of fucoxanthin expands from 450–540&nbsp;nm to 390–580&nbsp;nm, a range that is useful in [[aquatic environment]]s.<ref>{{cite journal | vauthors = Premvardhan L, Sandberg DJ, Fey H, Birge RR, Büchel C, van Grondelle R | title = The charge-transfer properties of the S2 state of fucoxanthin in solution and in fucoxanthin chlorophyll-a/c2 protein (FCP) based on stark spectroscopy and molecular-orbital theory | journal = The Journal of Physical Chemistry B | volume = 112 | issue = 37 | pages = 11838–53 | date = September 2008 | pmid = 18722413 | pmc = 2844098 | doi = 10.1021/jp802689p }}</ref>