Spheroidene

{{Chembox | Reference =  | Name = all-''trans''-spheroidene | IUPACName = (3''E'')-1-Methoxy-3,4-didehydro-1,2,7',8'-tetrahydro-ψ,ψ-carotene | PIN = | SystematicName = (6''E'',10''E'',12''E'',14''E'',16''E'',18''E'',20''E'',22''E'',24''E'',26''E'',28''E'')-31-methoxy-2,6,10,14,19,23,27,31-octamethyldotriaconta-2,6,10,12,14,16,18,20,22,24,26,28-dodecaene | OtherNames = {{Unbulleted list | Pigment Y }} | data page pagename =  | ImageFile = Spheroidene.svg | ImageSize = 300px | ImageAlt = Spheroidene skeletal formula | ImageName = All-trans-spheroidene | ImageCaption = | ImageFile1 = | ImageSize1 = | ImageAlt1 = | ImageName1 = | ImageCaption1 = | ImageFile2 = | ImageSize2 = | ImageAlt2 = | ImageName2 = | ImageCaption2 = | ImageFile3 = | ImageSize3 = | ImageAlt3 = | ImageName3 = | ImageFileL1 = | ImageSizeL1 = | ImageAltL1 = | ImageNameL1 = | ImageFileR1 = | ImageSizeR1 = | ImageAltR1 = | ImageNameR1 = | ImageFileL2 = | ImageSizeL2 = | ImageAltL2 = | ImageNameL2 = | ImageFileR2 = | ImageSizeR2 = | ImageAltR2 = | ImageNameR2 =  | Section1 = {{Chembox Identifiers | 3DMet = | Abbreviations = | Beilstein = | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 13836-61-8 | CASNo_Comment = | CASNoOther = | ChEBI = 35330 | ChemSpiderID = 4898273 | EINECS = | EC_number = | EC_number_Comment= | Gmelin = | InChI = 1S/C41H60O/c1-34(2)20-14-23-37(5)26-17-29-38(6)27-15-24-35(3)21-12-13-22-36(4)25-16-28-39(7)30-18-31-40(8)32-19-33-41(9,10)42-11/h12-13,15-16,18-22,24-28,30-32H,14,17,23,29,33H2,1-11H3/b13-12+,24-15+,25-16+,30-18+,32-19+,35-21+,36-22+,37-26+,38-27+,39-28+,40-31+ | StdInChIKey = FJOCMTHZSURUFA-AXYGSFPTSA-N | KEGG = C15900 | MeSHName = spheroidene | PubChem = 6368932 | RTECS = | SMILES = CC(=CCC/C(=C/CC/C(=C/C=C/C(=C/C=C/C=C(\C)/C=C/C=C(\C)/C=C/C=C(\C)/C=C/CC(C)(C)OC)/C)/C)/C)C | UNNumber = }} | Section2 = {{Chembox Properties | C=41 | H=60 | O=1 | AtmosphericOHRateConstant = | Appearance = | BoilingPt = | BoilingPtC = | BoilingPt_ref = | BoilingPt_notes= | Density = | Formula = | HenryConstant = | LogP = | MolarMass = | MeltingPt = | MeltingPtC = 135-138 | MeltingPt_ref = | MeltingPt_notes= | pKa = | pKb = | Solubility = | SolubleOther = | Solvent = | VaporPressure = }} | Section3 = {{Chembox Structure | Coordination = | CrystalStruct = | MolShape = }} }} '''Spheroidene''' is a carotenoid pigment. It is a component of the photosynthetic reaction center of certain purple bacteria of the ''Rhodospirillaceae'' family, including ''Rhodobacter sphaeroides'' and ''Rhodopseudomonas sphaeroides''.<ref name=Harrison>{{cite journal |last1=Harrison |first1=D.M. |date=1986 |title=The biosynthesis of carotenoids |url= |journal=Natural Product Reports |volume=3 |issue=3 |pages=205–215 |doi=10.1039/np9860300205 |pmid=3534642 }}</ref><ref name = Jackman>{{cite journal |last1=Barber |first1=M.S. |last2=Jackman |first2=L.M. |last3=Manchand |first3=P.S. |last4=Weedon |first4=B.C.L.|date=1966 |title=Carotenoids and related compounds. Part XVI. Structural and synthetic studies on spirilloxanthin, chloroxanthin, spheroidene, and spheroidenone. |journal=Journal of the Chemical Society C |volume= |issue= |pages=2166–2176 |doi=10.1039/j39660002166}}</ref> Like other carotenoids, it is a tetraterpenoid. In purified form, it is a brick-red solid soluble in benzene.<ref name=Jackman />

Spheroidene was discovered by microbiologist C. B. van Niel, who named it "pigment Y". It was renamed by Basil Weedon, who was the first to prepare it synthetically, and to determine its structure, in the mid-1960s.<ref name=Jackman />

==Function== Spheroidene is bound to the type II photosynthetic reaction center of purple bacteria, and together with the bacteriochlorophyll forms part of the light-harvesting complex. Spheroidene has two major functions in the complex. First, it absorbs visible light in the blue-green part of the visible spectrum (320–500 nm),<ref name=Jackman /> where bacteriochlorophyll has little absorbance. It then transfers energy to the bacteriochlorophyll via singlet–singlet energy transfer. In this manner the reaction center is able to harness more of the visible light spectrum than would be possible with bacteriochlorophyll alone.<ref name=Hashimoto>{{cite book |last1=Hashimoto |first1=Hideki |last2=Uragami |first2=Chiasa |last3=Cogdell |first3=Richard J. |chapter=Carotenoids and Photosynthesis |series=Subcellular Biochemistry |date=2016 |title=Carotenoids in Nature |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-39126-7_4 |volume=79 |pages=111–139 |pmid=27485220 |doi=10.1007/978-3-319-39126-7_4 |isbn=978-3-319-39124-3 }}</ref> Second, spheroidene quenches excited singlet states of bacteriochlorophyll by forming a stable triplet state. This quenching helps to prevent the formation of harmful singlet oxygen.<ref name=Frank>{{cite journal |last1=Frank |first1=Harry A. |last2=Cogdell |first2=Richard J. |date=1996 |title=Carotenoids in photosynthesis |journal=Photochemistry and Photobiology|volume=63 |issue=3 |pages=257–264 |issn=0031-8655 |pmid=8881328 |doi=10.1111/j.1751-1097.1996.tb03022.x |s2cid=1900488 }}</ref><ref name=Maresca>{{cite journal |last1=Maresca |first1=Julia A. |last2=Graham |first2=Joel E. |last3=Bryant |first3=Donald A. |date=2008 |title=The biochemical basis for structural diversity in the carotenoids of chlorophototrophic bacteria |journal=Photosynthesis Research|volume=97 |issue=2 |pages=121–140 |pmid=18535920 |doi=10.1007/s11120-008-9312-3|s2cid=2056720 }}</ref> Other functions of spheroidene may include scavenging of singlet oxygen, nonradiative dissipation of excess light energy, and structural stabilization of the photosystem proteins.<ref name=Frank />

Spheroidene is thought to exist as the 15,15'-''cis'' isomer, and not the all-''trans'' isomer commonly shown in the literature, in native photosynthetic reaction centers.<ref name="Mathies">{{cite journal|last1=Mathies|first1=Guinevere|last2=van Hemert|first2=Marc C.|last3=Gast|first3=Peter|last4=Gupta|first4=Karthick B. Sai Sankar|last5=Frank|first5=Harry A.|last6=Lugtenburg|first6=Johan|last7=Groenen|first7=Edgar J.J.|title=Configuration of spheroidene in the photosynthetic reaction center of Rhodobacter spheroides: A comparison of wild-type and reconstituted R26|journal=Journal of Physical Chemistry A|volume=115|issue=34|year=2011|pages=9552–9556|issn=1089-5639|doi=10.1021/jp112413d|pmid=21604722 |bibcode=2011JPCA..115.9552M |hdl=1887/3570972 |hdl-access=free}}</ref>

==Biosynthesis== The proteins involved in spheroidene biosynthesis are encoded by a gene cluster.<ref name=Naylor>{{cite journal|last1=Naylor |first1=Grant William |last2=Addlesee |first2=Hugh Alistair |last3=Gibson |first3=Lucien Charles Donald |last4=Hunter |first4=Christopher Neil |title=The photosynthesis gene cluster of ''Rhodobacter sphaeroides''|journal=Photosynthesis Research |volume=62 |issue=2–3 |year=1999|pages=121–139 |issn=0166-8595|doi=10.1023/A:1006350405674|s2cid=20340930 }}</ref> Geranylgeranyl pyrophosphate (GGPP) is the precursor to spheroidene and the other carotenoids; two molecules of GGPP condense to form the symmetric tetraterpene phytoene. This molecule then undergoes three desaturations to form neurosporene, which is then hydroxylated, desaturated again, and methoxylated to produce spheroidene. In some species, spheroidene is further oxygenated to produce the ketone spheroidenone.<ref name=Maresca />

== References ==

Category:Carotenoids Category:Photosynthetic pigments Category:Methoxy compounds