Misplaced Pages

Retinal: Difference between revisions

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.
Browse history interactively
Page 1
Page 2
← Previous editContent deleted Content addedVisualWikitext
Revision as of 16:21, 10 August 2011 editCheMoBot (talk | contribs)Bots141,565 edits Updating {{chembox}} (no changed fields - added verified revid - updated 'ChemSpiderID_Ref', 'DrugBank_Ref', 'UNII_Ref', 'ChEMBL_Ref', 'ChEBI_Ref', 'KEGG_Ref', 'StdInChI_Ref', 'StdInChIKey_Ref', 'ChEBI_Ref') per [[Misplaced Pages:WikiProject Chemicals/Chem← Previous edit Latest revision as of 03:35, 29 November 2024 edit undoHairy Dude (talk | contribs)Extended confirmed users86,489 edits →Vitamin A metabolism: {{block indent}}Tags: Mobile edit Mobile web edit Advanced mobile edit 
(155 intermediate revisions by 80 users not shown)
Line 1: Line 1:
{{short description|Vitamin A aldehyde, a polyene chromophore}}
{{chembox
{{Distinguish|Retinol}}
| verifiedrevid = 444084005
{{About|the molecule|the anatomical feature|Retina}}
| Name = All-trans-retinal
{{Chembox
| ImageFile = all-trans-Retinal2.svg
| Watchedfields = changed
| ImageSize = 350px
| verifiedrevid = 444085949
| IUPACName = (2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraenal
| Name = All-trans-retinal
| OtherNames = retinaldehyde; vitamin A aldehyde; RAL
| ImageFile = All-trans-Retinal.svg
| Section1 = {{Chembox Identifiers
| ImageSize = 250
| ImageAlt = Skeletal formula of retinal
| ImageFile1 = Retinal 3D ball.png
| ImageSize1 = 260
| ImageAlt1 = Ball-and-stick model of the retinal molecule
| IUPACName = Retinal
| SystematicName = (2''E'',4''E'',6''E'',8''E'')-3,7-Dimethyl-9-(2,6,6-trimethylcyclohex-1-en-1-yl)nona-2,4,6,8-tetraenal
| OtherNames = {{Bulleted list|Retinene|Retinaldehyde|Vitamin A aldehyde|RAL}}
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}} | CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 116-31-4 | CASNo = 116-31-4
| PubChem = 1070
| UNII_Ref = {{fdacite|correct|FDA}} | UNII_Ref = {{fdacite|correct|FDA}}
| UNII = RR725D715M | UNII = RR725D715M
| PubChem = 638015
| ChemSpiderID = 553582
| ChEBI = 17898
| StdInChI = 1S/C20H28O/c1-16(8-6-9-17(2)13-15-21)11-12-19-18(3)10-7-14-20(19,4)5/h6,8-9,11-13,15H,7,10,14H2,1-5H3/b9-6+,12-11+,16-8+,17-13+
| StdInChIKey = NCYCYZXNIZJOKI-OVSJKPMPSA-N
| SMILES = CC1=C(C(CCC1)(C)C)/C=C/C(=C/C=C/C(=C/C=O)/C)/C}} | SMILES = CC1=C(C(CCC1)(C)C)/C=C/C(=C/C=C/C(=C/C=O)/C)/C}}
| Section2 = {{Chembox Properties |Section2={{Chembox Properties
| Formula = C<sub>20</sub>H<sub>28</sub>O | C=20 | H=28 | O=1
| Appearance = Orange crystals from ]<ref name="Merck">''Merck Index'', 13th Edition, '''8249'''</ref>
| MolarMass= 284.436 g/mol
| Density =
| Appearance = orange crystals from petr ether <ref name="Merck">''Merck Index'', 13th Edition, '''8249'''.</ref>
| MeltingPtC = 61 to 64
| Density=
| MeltingPt = 61-64 °C <ref name="Merck"/> | MeltingPt_ref = <ref name="Merck"/>
| BoilingPt = | BoilingPt =
| Solubility = nearly insoluble | Solubility = Nearly insoluble
| SolubleOther = soluble | SolubleOther = Soluble
| Solvent = fat}} | Solvent = fat}}
| Section7 = {{Chembox Hazards |Section7={{Chembox Hazards
| MainHazards = | MainHazards =
| FlashPt = | FlashPt =
| Autoignition = }} | AutoignitionPt = }}
| Section8 = {{Chembox Related |Section8={{Chembox Related
| OtherFunctn = | OtherFunction =
| Function = | OtherFunction_label =
| OtherCpds = ]; ]; ]; ]; 3-hydroxyretinal; 4-hydroxyretinal}} | OtherCompounds = ]; ]; ]; ]; 3-hydroxyretinal; 4-hydroxyretinal}}
}} }}


'''Retinal''', also called '''retinaldehyde''' or '''vitamin A ]''', is one of the many forms of vitamin A (the number of which varies from species to species). Retinal is a ] ], and bound to proteins called ]s, is the chemical basis of ] vision. Bound to proteins called type 1 ]s, retinal allows certain microorganisms to convert light into metabolic energy. '''Retinal''' (also known as '''retinaldehyde''') is a ] ]. Retinal, bound to proteins called ]s, is the chemical basis of ], the light-detection stage of ] (vision).


Some microorganisms use retinal to convert light into metabolic energy. One study suggests that approximately three billion years ago, most living organisms on Earth used retinal, rather than ], to convert sunlight into energy. Because retinal absorbs mostly green light and transmits purple light, this gave rise to the ].<ref>{{Cite journal |last1=DasSarma |first1=Shiladitya |last2=Schwieterman |first2=Edward W. |date=2018 |title=Early evolution of purple retinal pigments on Earth and implications for exoplanet biosignatures |journal=International Journal of Astrobiology |language=en |publication-date=2018-10-11 |volume=20 |issue=3 |pages=241–250 |doi=10.1017/S1473550418000423 |s2cid=119341330 |issn=1473-5504|doi-access=free |arxiv=1810.05150 }}</ref>
Vertebrate animals ingest retinal directly from meat, or produce retinal from one of four ]s (], ], ], and beta-]), which they must obtain from ] or other ] organisms (no other ]s can be converted by animals to retinal, and some carnivores cannot convert any carotenoids at all). The other main forms of vitamin A, ], and a partially active form ], may both be produced from retinal.


Retinal itself is considered to be a form of ] when eaten by an animal. There are many forms of vitamin A, all of which are converted to retinal, which cannot be made without them. The number of different molecules that can be converted to retinal varies from species to species. Retinal was originally called ''']''',<ref name=Wald1934>{{cite journal |last1=Wald |first1=George |title=Carotenoids and the Vitamin A Cycle in Vision |journal=Nature |date=14 July 1934 |volume=134 |issue=3376 |pages=65 |doi=10.1038/134065a0 |bibcode=1934Natur.134...65W |s2cid=4022911|doi-access=free }}</ref> and was renamed<ref name=Wald1968>{{cite journal |last1=Wald |first1=G. |title=Molecular basis of visual excitation |journal=Science |date=11 October 1968 |volume=162 |issue=3850 |pages=230–9 |pmid=4877437 |doi=10.1126/science.162.3850.230 |bibcode=1968Sci...162..230W}}</ref> after it was discovered to be '''vitamin A ]'''.<ref name=Morton1944>{{cite journal |last1=MORTON |first1=R. A. |last2=GOODWIN |first2=T. W. |title=Preparation of Retinene in Vitro |journal=Nature |date=1 April 1944 |volume=153 |issue=3883 |pages=405–406 |doi=10.1038/153405a0 |bibcode=1944Natur.153..405M |s2cid=4111460}}</ref><ref name=Ball1946>{{cite journal |last1=Ball |first1=S. |last2=Goodwin |first2=T. W. |last3=Morton |first3=R. A. |title=Retinene1-vitamin A aldehyde. |journal=The Biochemical Journal |date=1946 |volume=40 |issue=5–6 |pages=lix |pmid=20341217}}</ref>
Invertebrates such as insects and squid use hydroxylated forms of retinal in their visual systems, which derive from conversion from other xanthophylls.


] animals ingest retinal directly from meat, or they produce retinal from ]s – either from ] or ] – both of which are ]s. They also produce it from ], a type of ]. These carotenoids must be obtained from plants or other ] organisms. No other carotenoids can be converted by animals to retinal. Some carnivores cannot convert any carotenoids at all. The other main forms of vitamin A – ] and a partially active form, ] – may both be produced from retinal.
==Vitamin A metabolism==


]s such as ]s and ] use hydroxylated forms of retinal in their visual systems, which derive from conversion from other ].
Living organisms produce retinal (RAL) by irreversible oxidative cleavage of carotenoids.<ref name="von Lintig">{{cite journal |last=von Lintig |first=Johannes |last2=Vogt |first2=Klaus |year=2000 |title=Filling the Gap in Vitamin A Research: Molecular Identification of An Enzyme Cleaving Beta-carotene to Retinal |journal=Journal of Biological Chemistry |volume=275 |issue=16 |pages=11915–11920 |publisher=ASBMB |pmid=10766819 |doi=10.1074/jbc.275.16.11915}}</ref>
For example


==Vitamin A metabolism==
:] + O<sub>2</sub> &rarr; 2 retinal


catalyzed by a ]<ref>{{cite journal |last=Woggon |first=Wolf-D. |year=2002 |title=Oxidative cleavage of carotenoids catalyzed by enzyme models and beta-carotene 15,15´-monooxygenase |journal=Pure and Applied Chemistry |volume=74 |issue=8 |pages=1397–1408 |publisher=IUPAC |doi=10.1351/pac200274081397}}</ref> Living organisms produce retinal by irreversible oxidative cleavage of carotenoids.<ref name="von Lintig">{{cite journal |last1=von Lintig |first1=Johannes |last2=Vogt |first2=Klaus |year=2000 |title=Filling the Gap in Vitamin A Research: Molecular Identification of An Enzyme Cleaving Beta-carotene to Retinal |journal=Journal of Biological Chemistry |volume=275 |issue=16 |pages=11915–11920 |pmid=10766819 |doi=10.1074/jbc.275.16.11915 |doi-access=free}}</ref>
or a beta-carotene 15,15'-dioxygenase.<ref name="Kim09">{{cite journal |last=Kim |first=Yeong-Su |last2=Kim |first2=Nam-Hee |last3=Yeom |first3=Soo-Jin |last4=Kim |first4=Seon-Won |last5=Oh |first5=Deok-Kun |year=2009 |title=In Vitro Characterization of a Recombinant Blh Protein from an Uncultured Marine Bacterium as a beta-Carotene 15,15'-Dioxygenase |journal=Journal of Biological Chemistry |volume=284 |issue=23 |pages=15781–93 |publisher=ASBMB |pmid=19366683 |doi=10.1074/jbc.M109.002618 |pmc=2708875}}</ref>
Just as carotenoids are the precursors of retinal, retinal is the precursor of the other forms of vitamin A. Retinal is interconvertible with ] (ROL), the transport and storage form of vitamin A


For example:
:retinal + ] + H<sup>+</sup> {{eqm}} retinol + NADP<sup>+</sup>
{{block indent|] + O<sub>2</sub> → 2 retinal,}}
:retinol + ]<sup>+</sup> {{eqm}} retinal + NADH + H<sup>+</sup>


catalyzed by ]s (RDHs)<ref>{{cite journal |last=Lidén |first=Martin |last2=Eriksson |first2=Ulf |year=2006 |title=Understanding Retinol Metabolism: Structure and Function of Retinol Dehydrogenases |journal=Journal of Biological Chemistry |volume=281 |issue=19 |pages=13001–13004 |publisher=ASBMB |doi=10.1074/jbc.R500027200 |pmid=16428379}}</ref> and ]s (ADHs).<ref name="Duester">{{cite journal |last1=Duester |first1=G |title=Retinoic acid synthesis and signaling during early organogenesis |journal=Cell |volume=134 |issue=6 |pages=921–31 |year=2008 |month=September |pmid=18805086 |pmc=2632951 |doi=10.1016/j.cell.2008.09.002 }}</ref> catalyzed by a ]<ref>{{cite journal |last=Woggon |first=Wolf-D. |year=2002 |title=Oxidative cleavage of carotenoids catalyzed by enzyme models and beta-carotene 15,15'-monooxygenase |journal=Pure and Applied Chemistry |volume=74 |issue=8 |pages=1397–1408 |doi=10.1351/pac200274081397 |doi-access=free}}</ref> or a beta-carotene 15,15'-dioxygenase.<ref name="Kim09">{{cite journal |last1=Kim |first1=Yeong-Su |last2=Kim |first2=Nam-Hee |last3=Yeom |first3=Soo-Jin |last4=Kim |first4=Seon-Won |last5=Oh |first5=Deok-Kun |year=2009 |title=In Vitro Characterization of a Recombinant Blh Protein from an Uncultured Marine Bacterium as a β-Carotene 15,15′-Dioxygenase |journal=Journal of Biological Chemistry |volume=284 |issue=23 |pages=15781–93 |pmid=19366683 |doi=10.1074/jbc.M109.002618 |pmc=2708875|doi-access=free }}</ref>
Retinol is called vitamin A ], or more often, simply vitamin A. Retinal can also be oxidized to ] (RA)


Just as carotenoids are the precursors of retinal, retinal is the precursor of the other forms of vitamin A. Retinal is interconvertible with ], the transport and storage form of vitamin A:
:retinal + NAD<sup>+</sup> + H<sub>2</sub>O &rarr; retinoic acid + NADH + H<sup>+</sup> (catalyzed by RALDH)
{{block indent|retinal + ] + H<sup>+</sup> {{eqm}} retinol + NADP<sup>+</sup>}}
:retinal + O<sub>2</sub> + H<sub>2</sub>O &rarr; retinoic acid + H<sub>2</sub>O<sub>2</sub> (catalyzed by retinal oxidase)
{{block indent|retinol + ]<sup>+</sup> {{eqm}} retinal + NADH + H<sup>+</sup>,}}


catalyzed by ]s<ref>{{cite journal |last=Lin |first=Min |last2=Zhang |first2=Min |last3=Abraham |first3=Michael |last4=Smith |first4=Susan M. |last5=Napoli |first5=Joseph L. |year=2003 |title=Mouse Retinal Dehydrogenase 4 (RALDH4), Molecular Cloning, Cellular Expression, and Activity in 9-cis-Retinoic Acid Biosynthesis in Intact Cells |journal=Journal of Biological Chemistry |volume=278 |issue=11 |pages=9856–9861 |publisher=ASBMB |doi=10.1074/jbc.M211417200 |pmid=12519776}}</ref> also known as retinaldehyde dehydrogenases (RALDHs)<ref name="Duester"/> catalyzed by ]s (RDHs)<ref>{{cite journal |last1=Lidén |first1=M |last2=Eriksson |first2=U |year=2006 |title=Understanding Retinol Metabolism: Structure and Function of Retinol Dehydrogenases |journal=Journal of Biological Chemistry |volume=281 |issue=19 |pages=13001–04 |doi=10.1074/jbc.R500027200 |pmid=16428379 |doi-access=free}}</ref> and ]s (ADHs).<ref name="Duester">{{cite journal |last1=Duester |first1=G |title=Retinoic Acid Synthesis and Signaling during Early Organogenesis |journal=Cell |volume=134 |issue=6 |pages=921–31 |date=September 2008 |pmid=18805086 |pmc=2632951 |doi=10.1016/j.cell.2008.09.002}}</ref>
as well as ]s.<ref>{{cite web |url=http://www.genome.ad.jp/dbget-bin/www_bget?enzyme+1.2.3.11 |title=KEGG ENZYME: 1.2.3.11 retinal oxidase |accessdate=2009-03-10 }}</ref>
Retinoic acid, sometimes called vitamin A ], is an important signaling molecule and hormone in vertebrate animals.


Retinol is called vitamin A ] or, more often, simply vitamin A. Retinal can also be oxidized to ]:
== Vision ==
{{block indent|retinal + NAD<sup>+</sup> + H<sub>2</sub>O → retinoic acid + NADH + H<sup>+</sup> (catalyzed by RALDH)}}
]]]
{{block indent|retinal + O<sub>2</sub> + H<sub>2</sub>O → retinoic acid + H<sub>2</sub>O<sub>2</sub> (catalyzed by retinal oxidase),}}


catalyzed by ]s<ref>{{cite journal |last1=Lin |first1=Min |last2=Zhang |first2=Min |last3=Abraham |first3=Michael |last4=Smith |first4=Susan M. |last5=Napoli |first5=Joseph L. |year=2003 |title=Mouse Retinal Dehydrogenase 4 (RALDH4), Molecular Cloning, Cellular Expression, and Activity in 9-cis-Retinoic Acid Biosynthesis in Intact Cells |journal=Journal of Biological Chemistry |volume=278 |issue=11 |pages=9856–9861 |doi=10.1074/jbc.M211417200 |pmid=12519776 |doi-access=free}}</ref> also known as retinaldehyde dehydrogenases (RALDHs)<ref name="Duester"/> as well as ]s.<ref>{{cite web |url=https://www.genome.jp/dbget-bin/www_bget?enzyme+1.2.3.11 |title=KEGG ENZYME: 1.2.3.11 retinal oxidase |access-date=2009-03-10}}</ref>
Vision begins with the ] of retinal. When the 11-cis-retinal chromophore absorbs a ] it isomerizes from the 11-cis state to the all-trans state. The absorbance spectrum of the chromophore depends on its interactions with the ] protein to which it is bound; different opsins produce different absorbance spectra.


Retinoic acid, sometimes called vitamin A ], is an important signaling molecule and hormone in vertebrate animals.
=== Opsins ===


==Vision==
Opsins are proteins and the retinal-binding visual pigments found in the ] in the ]s of eyes. An opsin is arranged into a bundle of seven transmembrane ] connected by six loops. In ] the opsin molecules are embedded in the membranes of the disks which are entirely inside of the cell. The ] head of the molecule extends into the interior of the disk, and the ] tail extends into the cytoplasm of the cell. In cone cells the disks are defined by the cell's ] so that the N-terminus head extends outside of the cell. Retinal binds covalently to a ] on the transmembrane helix nearest the C-terminus of the protein through a ] linkage. Formation of the Schiff base linkage involves removing the oxygen atom from retinal and two hydrogen atoms from the free amino group of lysine, giving H<sub>2</sub>O. '''Retinylidene''' is the divalent group formed by removing the oxygen atom from retinal, and so opsins have been called ]s.
Retinal is a ]. In the ], retinal begins in an 11-''cis''-retinal configuration, which — upon capturing a ] of the correct wavelength — straightens out into an all-''trans''-retinal configuration. This configuration change pushes against an opsin protein in the ], which triggers a chemical signaling cascade, which results in ] of light or images by the brain. The absorbance spectrum of the chromophore depends on its interactions with the opsin protein to which it is bound, so that different retinal-opsin complexes will absorb photons of different wavelengths (i.e., different colors of light).


===Opsins===
Opsins are prototypical ]s (GPCRs).<ref>{{cite journal |last=Lamb |first=T D |year=1996 |title=Gain and kinetics of activation in the G-protein cascade of phototransduction |journal=Proceedings of the National Academy of Sciences |volume=93 |issue=2 |pages=566–570 |publisher= |pmid=8570596 |doi=10.1073/pnas.93.2.566 |pmc=40092}}</ref> Bovine rhodopsin, the opsin of the rod cells of cattle, was the first GPCR to have its ] determined.<ref name="Palczewski">{{cite journal |last=Palczewski |first=Krzysztof |last2=Kumasaka |first2= Takashi |last3=et al. |authorlink=Krzysztof Palczewski |year=2000 |title=Crystal Structure of Rhodopsin: A G Protein-Coupled Receptor |journal=Science |volume=289 |issue=5480 |pages=739–745 |publisher=AAAS |doi=10.1126/science.289.5480.739 |pmid=10926528 |first3=T |last4=Behnke |first4=CA |last5=Motoshima |first5=H |last6=Fox |first6=BA |last7=Le Trong |first7=I |last8=Teller |first8=DC |last9=Okada |first9=T}}</ref>
]
Bovine rhodopsin contains 348 amino acid residues. The retinal chromophore binds at Lys<sup>296</sup>.
] (rainbow-colored) embedded in a ] (heads red and tails blue) with ] below it. G<sub>t</sub>α is colored red, G<sub>t</sub>β blue, and G<sub>t</sub>γ yellow. There is a bound ] molecule in the G<sub>t</sub>α-subunit and a bound '''retinal''' (black) in the rhodopsin. The ] terminus of rhodopsin is red and the ] blue. Anchoring of transducin to the membrane has been drawn in black.]]


Retinal is bound to ]s, which are ]s (GPCRs).<ref name=Casey1988>{{cite journal |last1=Casey |first1=P J |last2=Gilman |first2=A G |title=G protein involvement in receptor-effector coupling. |journal=Journal of Biological Chemistry |date=February 1988 |volume=263 |issue=6 |pages=2577–2580 |doi=10.1016/s0021-9258(18)69103-3 |pmid=2830256|s2cid=38970721 |doi-access=free }}</ref><ref name=Attwood1994>{{cite journal |last1=Attwood |first1=T. K. |last2=Findlay |first2=J. B. C. |title=Fingerprinting G-protein-coupled receptors |journal=Protein Engineering, Design and Selection |date=1994 |volume=7 |issue=2 |pages=195–203 |doi=10.1093/protein/7.2.195|pmid=8170923 }}</ref> Opsins, like other GPCRs, have seven transmembrane ] connected by six loops. They are found in the ]s in the ] of eye. The opsin in the vertebrate ]s is ]. The rods form disks, which contain the rhodopsin molecules in their membranes and which are entirely inside of the cell. The ] head of the molecule extends into the interior of the disk, and the ] tail extends into the cytoplasm of the cell. The opsins in the ]s are ], ], and ]. The cones form incomplete disks that are part of the ], so that the N-terminus head extends outside of the cell. In opsins, retinal binds covalently to a ]<ref>{{cite journal |last1=Bownds |first1=Deric |title=Site of Attachment of Retinal in Rhodopsin |journal=Nature |date=December 1967 |volume=216 |issue=5121 |pages=1178–1181 |doi=10.1038/2161178a0 |pmid=4294735|bibcode=1967Natur.216.1178B |s2cid=1657759 }}</ref> in the seventh transmembrane helix<ref>{{cite journal |last1=Hargrave |first1=P. A. |last2=McDowell |first2=J. H. |last3=Curtis |first3=Donna R. |last4=Wang |first4=Janet K. |last5=Juszczak |first5=Elizabeth |last6=Fong |first6=Shao-Ling |last7=Mohana Rao |first7=J. K. |last8=Argos |first8=P. |title=The structure of bovine rhodopsin |journal=Biophysics of Structure and Mechanism |date=1983 |volume=9 |issue=4 |pages=235–244 |doi=10.1007/BF00535659 |pmid=6342691|s2cid=20407577 }}</ref><ref name=Palczewski2000>{{cite journal | vauthors = Palczewski K, Kumasaka T, Hori T, Behnke CA, Motoshima H, Fox BA, Le Trong I, Teller DC, Okada T, Stenkamp RE, Yamamoto M, Miyano M | display-authors = 6 | title = Crystal structure of rhodopsin: A G protein-coupled receptor | journal = Science | volume = 289 | issue = 5480 | pages = 739–45 | date = August 2000 | pmid = 10926528 | doi = 10.1126/science.289.5480.739 | citeseerx = 10.1.1.1012.2275 | bibcode = 2000Sci...289..739P }}</ref><ref name=Murakami2008>{{cite journal | vauthors = Murakami M, Kouyama T | title = Crystal structure of squid rhodopsin | journal = Nature | volume = 453 | issue = 7193 | pages = 363–7 | date = May 2008 | pmid = 18480818 | doi = 10.1038/nature06925 | bibcode = 2008Natur.453..363M | s2cid = 4339970 }}</ref> through a ].<ref>{{cite journal |last1=Collins |first1=F. D. |title=Rhodopsin and Indicator Yellow |journal=Nature |date=March 1953 |volume=171 |issue=4350 |pages=469–471 |doi=10.1038/171469a0 |pmid=13046517|bibcode=1953Natur.171..469C |s2cid=4152360 }}</ref><ref>{{cite journal |last1=Pitt |first1=G. A. J. |last2=Collins |first2=F. D. |last3=Morton |first3=R. A. |last4=Stok |first4=Pauline |title=Studies on rhodopsin. 8. Retinylidenemethylamine, an indicator yellow analogue |journal=Biochemical Journal |date=1 January 1955 |volume=59 |issue=1 |pages=122–128 |doi=10.1042/bj0590122 |pmid=14351151|pmc=1216098 }}</ref> Forming the Schiff base linkage involves removing the oxygen atom from retinal and two hydrogen atoms from the free amino group of lysine, giving H<sub>2</sub>O. Retinylidene is the divalent group formed by removing the oxygen atom from retinal, and so opsins have been called ]s.
Although mammals use retinal exclusively as the opsin chromophore, other groups of animals additionally use four chromophores closely related to retinal. These are (3,4)-didehydroretinal, (3R)-3-hydroxyretinal, (3S)-3-hydroxyretinal, and (4R)-4-hydroxyretinal. Many fish and amphibians use (3,4)-didehydroretinal, also called ]. With the exception of the ]n suborder ], the so-called higher flies, all ] examined use the R ] of 3-hydroxyretinal. The R enantiomer is to be expected if 3-hydroxyretinal is produced directly from ] carotenoids. Cyclorrhaphans, including ], use (3S)-3-hydroxyretinal.<ref>{{cite journal |last=Seki |first=Takaharu |last2=Isono |first2=Kunio |last3=Ito |first3=Masayoshi |last4=Katsuta |first4=Yuko |year=1994 |title=Flies in the Group Cyclorrhapha Use (3S)-3-Hydroxyretinal as a Unique Visual Pigment Chromophore |journal=European Journal of Biochemistry |volume=226 |issue=2 |pages=691–696 |publisher=Wiley |doi=10.1111/j.1432-1033.1994.tb20097.x |pmid=8001586}}</ref><ref>{{cite journal |last=Seki |first=Takaharu |last2=Isono |first2=Kunio |last3=Ozaki |first3=Kaoru |last4=Tsukahara |first4=Yasuo |last5=Shibata-Katsuta |first5=Yuko |last6=Ito |first6=Masayoshi |last7=Irie |first7=Toshiaki |last8=Katagiri |first8=Masanao |last9= |first9= |year=1998 |title=The metabolic pathway of visual pigment chromophore formation in Drosophila melanogaster: All-trans (3S)-3-hydroxyretinal is formed from all-trans retinal via (3R)-3-hydroxyretinal in the dark |journal=European Journal of Biochemistry |volume=257 |issue=2 |pages=522–527 |publisher=Wiley |doi=10.1046/j.1432-1327.1998.2570522.x |pmid=9826202}}</ref>
] have been found to use (4R)-4-hydroxyretinal.


Opsins are prototypical ]s (GPCRs).<ref>{{cite journal |last=Lamb |first=T D |year=1996 |title=Gain and kinetics of activation in the G-protein cascade of phototransduction |journal=Proceedings of the National Academy of Sciences |volume=93 |issue=2 |pages=566–570 |pmid=8570596 |doi=10.1073/pnas.93.2.566 |pmc=40092 |bibcode=1996PNAS...93..566L|doi-access=free }}</ref> Cattle rhodopsin, the opsin of the rod cells, was the first GPCR to have its ]<ref name=Ovchinnikov1982>{{cite journal |last1=Ovchinnikov |first1=Yu.A. |title=Rhodopsin and bacteriorhodopsin: structure-function relationships |journal=FEBS Letters |date=8 November 1982 |volume=148 |issue=2 |pages=179–191 |doi=10.1016/0014-5793(82)80805-3 |pmid=6759163|s2cid=85819100 |doi-access=free |bibcode=1982FEBSL.148..179O }}</ref> and ] (via ]) determined.<ref name="Palczewski2000" /> ] rhodopsin contains 348 ] residues. Retinal binds as chromophore at Lys<sup>296</sup>.<ref name="Palczewski2000" /><ref name=Ovchinnikov1982 /> This lysine is conserved in almost all opsins, only a few opsins have lost it during ].<ref name=Guehmann2022>{{cite journal | vauthors = Gühmann M, Porter ML, Bok MJ | title = The Gluopsins: Opsins without the Retinal Binding Lysine | journal = Cells | volume = 11 | issue = 15 | pages = 2441 | date = August 2022 | pmid = 35954284 | doi = 10.3390/cells11152441 | pmc = 9368030 | doi-access = free }}</ref> Opsins without the retinal binding lysine are not light sensitive.<ref name=Katana2019>{{cite journal |last1=Katana |first1=Radoslaw |last2=Guan |first2=Chonglin |last3=Zanini |first3=Damiano |last4=Larsen |first4=Matthew E. |last5=Giraldo |first5=Diego |last6=Geurten |first6=Bart R.H. |last7=Schmidt |first7=Christoph F. |last8=Britt |first8=Steven G. |last9=Göpfert |first9=Martin C. |title=Chromophore-Independent Roles of Opsin Apoproteins in Drosophila Mechanoreceptors |journal=Current Biology |date=September 2019 |volume=29 |issue=17 |pages=2961–2969.e4 |doi=10.1016/j.cub.2019.07.036 |pmid=31447373|s2cid=201420079 |doi-access=free |bibcode=2019CBio...29E2961K }}</ref><ref name=Leung2020>{{cite journal |last1=Leung |first1=Nicole Y. |last2=Thakur |first2=Dhananjay P. |last3=Gurav |first3=Adishthi S. |last4=Kim |first4=Sang Hoon |last5=Di Pizio |first5=Antonella |last6=Niv |first6=Masha Y. |last7=Montell |first7=Craig |title=Functions of Opsins in Drosophila Taste |journal=Current Biology |date=April 2020 |volume=30 |issue=8 |pages=1367–1379.e6 |doi=10.1016/j.cub.2020.01.068 |pmid=32243853|pmc=7252503 |bibcode=2020CBio...30E1367L }}</ref><ref>{{cite journal | vauthors = Kumbalasiri T, Rollag MD, Isoldi MC, Castrucci AM, Provencio I | title = Melanopsin triggers the release of internal calcium stores in response to light | journal = Photochemistry and Photobiology | volume = 83 | issue = 2 | pages = 273–279 | date = March 2007 | pmid = 16961436 | doi = 10.1562/2006-07-11-RA-964 | s2cid = 23060331 }}</ref> Such opsins may have other functions.<ref name=Leung2020 /><ref name=Guehmann2022 />
=== Visual cycle ===


Although mammals use retinal exclusively as the opsin chromophore, other groups of animals additionally use four chromophores closely related to retinal: 3,4-didehydroretinal (vitamin A<sub>2</sub>), (3''R'')-3-hydroxyretinal, (3''S'')-3-hydroxyretinal (both vitamin A<sub>3</sub>), and (4''R'')-4-hydroxyretinal (vitamin A<sub>4</sub>). Many fish and amphibians use 3,4-didehydroretinal, also called ]. With the exception of the ]n suborder ] (the so-called higher flies), all ]s examined use the (''R'')-] of 3-hydroxyretinal. The (''R'')-enantiomer is to be expected if 3-hydroxyretinal is produced directly from ] carotenoids. Cyclorrhaphans, including '']'', use (3''S'')-3-hydroxyretinal.<ref>{{cite journal |last1=Seki |first1=Takaharu |last2=Isono |first2=Kunio |last3=Ito |first3=Masayoshi |last4=Katsuta |first4=Yuko |year=1994 |title=Flies in the Group Cyclorrhapha Use (3S)-3-Hydroxyretinal as a Unique Visual Pigment Chromophore |journal=European Journal of Biochemistry |volume=226 |issue=2 |pages=691–696 |doi=10.1111/j.1432-1033.1994.tb20097.x |pmid=8001586 |doi-access=}}</ref><ref>{{cite journal |last1=Seki |first1=Takaharu |last2=Isono |first2=Kunio |last3=Ozaki |first3=Kaoru |last4=Tsukahara |first4=Yasuo |last5=Shibata-Katsuta |first5=Yuko |last6=Ito |first6=Masayoshi |last7=Irie |first7=Toshiaki |last8=Katagiri |first8=Masanao |year=1998 |title=The metabolic pathway of visual pigment chromophore formation in Drosophila melanogaster: All-trans (3S)-3-hydroxyretinal is formed from all-trans retinal via (3R)-3-hydroxyretinal in the dark |journal=European Journal of Biochemistry |volume=257 |issue=2 |pages=522–527 |doi=10.1046/j.1432-1327.1998.2570522.x |pmid=9826202 |doi-access=free}}</ref> ] have been found to use (4''R'')-4-hydroxyretinal.
]
{{Clear}}


===Visual cycle===
The visual cycle is a circular ], which is the front-end of phototransduction. It regenerates 11-cis-retinal.
{{main|Visual cycle}}
]
The visual cycle is a circular ], which is the front-end of phototransduction. It regenerates 11-''cis''-retinal. For example, the visual cycle of mammalian rod cells is as follows:
#] + H<sub>2</sub>O → 11-''cis''-retinol + ]; ] isomerohydrolases;<ref>{{cite journal |last1=Moiseyev |first1=Gennadiy |last2=Chen |first2=Ying |last3=Takahashi |first3=Yusuke |last4=Wu |first4=Bill X. |last5=Ma |first5=Jian-xing |year=2005 |title=RPE65 is the isomerohydrolase in the retinoid visual cycle |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=35 |pages=12413–12418 |doi=10.1073/pnas.0503460102 |pmid=16116091 |pmc=1194921 |bibcode=2005PNAS..10212413M|doi-access=free }}</ref>
#] + NAD<sup>+</sup> → 11-''cis''-retinal + NADH + H<sup>+</sup>; 11-''cis''-retinol dehydrogenases;
#] + ] → ] + H<sub>2</sub>O; forms ] linkage to ], -CH=N<sup>+</sup>H-;
#rhodopsin + ] → ] II (i.e., 11-''cis'' ] to all-''trans''):
#:(rhodopsin + hν → photorhodopsin → bathorhodopsin → lumirhodopsin → metarhodopsin I → metarhodopsin II);
#] II + H<sub>2</sub>O → aporhodopsin + all-''trans''-retinal;
#] + NADPH + H<sup>+</sup> → all-''trans''-retinol + NADP<sup>+</sup>; all-''trans''-retinol ]s;
#all-''trans''-retinol + fatty acid → all-''trans''-retinyl ester + H<sub>2</sub>O; ]s (LRATs).<ref>{{cite journal |last1=Jin |first1=Minghao |last2=Yuan |first2=Quan |last3=Li |first3=Songhua |last4=Travis |first4=Gabriel H. |year=2007 |title=Role of LRAT on the Retinoid Isomerase Activity and Membrane Association of Rpe65 |journal=Journal of Biological Chemistry |volume=282 |issue=29 |pages=20915–20924 |doi=10.1074/jbc.M701432200 |pmid=17504753 |pmc=2747659|doi-access=free }}</ref>


Steps 3, 4, 5, and 6 occur in ]; Steps 1, 2, and 7 occur in ] (RPE) cells.
For example, the visual cycle of mammalian rod cells
#] + H<sub>2</sub>O → 11-cis-retinol + ]; ] isomerohydrolases<ref>{{cite journal |last=Moiseyev |first=Gennadiy |last2=Chen |first2=Ying |last3=Takahashi |first3=Yusuke |last4=Wu |first4=Bill X. |last5=Ma |first5=Jian-xing |year=2005 |title=RPE65 is the isomerohydrolase in the retinoid visual cycle |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=35 |pages=12413–12418 |publisher= |doi=10.1073/pnas.0503460102 |pmid=16116091 |pmc=1194921}}</ref>
#] + NAD<sup>+</sup> → 11-cis-retinal + NADH + H<sup>+</sup>; 11-cis-retinol dehydrogenases
#] + ] → ] + H<sub>2</sub>O; forms ] linkage to ], -CH=N<sup>+</sup>H-
#rhodopsin + hν → ]; 11-cis ] to all-trans
#:rhodopsin + hν → photorhodopsin → bathorhodopsin → lumirhodopsin → metarhodopsin I → ]
#] + H<sub>2</sub>O → aporhodopsin + all-trans-retinal
#] + NADPH + H<sup>+</sup> → all-trans-retinol + NADP<sup>+</sup>; all-trans-retinol ]
#all-trans-retinol + fatty acid → all-trans-retinyl ester + H<sub>2</sub>O; ]s (LRATs)<ref>{{cite journal |last=Jin |first=Minghao |last2=Yuan |first2=Quan |last3=Li |first3=Songhua |last4=Travis |first4=Gabriel H. |year=2007 |title=Role of LRAT on the Retinoid Isomerase Activity and Membrane Association of Rpe65 |journal=Journal of Biological Chemistry |volume=282 |issue=29 |pages=20915–20924 |publisher=ASBMB |doi=10.1074/jbc.M701432200 |pmid=17504753 |pmc=2747659}}</ref>


RPE65 isomerohydrolases are ] with beta-carotene monooxygenases;<ref name="von Lintig"/> the homologous ninaB enzyme in ''Drosophila'' has both retinal-forming carotenoid-oxygenase activity and all-''trans'' to 11-''cis'' isomerase activity.<ref name="Oberhauser08">{{cite journal |last1=Oberhauser |first1=Vitus |last2=Voolstra |first2=Olaf |last3=Bangert |first3=Annette |last4=von Lintig |first4=Johannes |last5=Vogt |first5=Klaus |year=2008 |title=NinaB combines carotenoid oxygenase and retinoid isomerase activity in a single polypeptide |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=48 |pages=19000–5 |doi=10.1073/pnas.0807805105 |pmid=19020100 |pmc=2596218 |bibcode=2008PNAS..10519000O|doi-access=free }}</ref>
Steps 3,4,5,6 occur in ]; Steps 1, 2, and 7 occur in ] (RPE) cells.


==Microbial rhodopsins==
] (rainbow colored) embedded in a ] (heads red and tails blue) with ] below it. G<sub>t</sub>α is colored red, G<sub>t</sub>β blue, and G<sub>t</sub>γ yellow. There is a bound ] molecule in the G<sub>t</sub>α-subunit and a bound '''retinal''' (black) in the rhodopsin. The ] terminus of rhodopsin is red and the ] blue. Anchoring of transducin to the membrane has been drawn in black.]]
{{Main article|Microbial rhodopsin}}

All-''trans''-retinal is also an essential component of ] opsins such as ], ], and ], which are important in ]l and ]l ]. In these molecules, light causes the all-''trans''-retinal to become 13-''cis'' retinal, which then cycles back to all-''trans''-retinal in the dark state. These proteins are not evolutionarily related to animal opsins and are not GPCRs; the fact that they both use retinal is a result of ].<ref name=13CIS>{{cite journal |doi=10.1016/S1011-1344(02)00245-2 |pmid=11960728 |title=All-trans to 13-cis retinal isomerization in light-adapted bacteriorhodopsin at acidic pH |year=2002 |last1=Chen |first1=De-Liang |last2=Wang |first2=Guang-yu |last3=Xu |first3=Bing |last4=Hu |first4=Kun-Sheng |journal=Journal of Photochemistry and Photobiology B: Biology |volume=66 |issue=3 |pages=188–194|bibcode=2002JPPB...66..188C }}</ref>
As it happens, RPE65 isomerohydrolases are ] with beta-carotene monooxygenases;<ref name="von Lintig"/>
the homologous ninaB enzyme in ''Drosophila'' has both retinal-forming carotenoid-oxygenase activity and all-trans to 11-cis isomerase activity.<ref name="Oberhauser08">{{cite journal |last=Oberhauser |first=Vitus |last2=Voolstra |first2=Olaf |last3=Bangert |first3=Annette |last4=von Lintig |first4=Johannes |last5=Vogt |first5=Klaus |year=2008 |title=NinaB combines carotenoid oxygenase and retinoid isomerase activity in a single polypeptide |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=48 |pages=19000–5 |publisher= |doi=10.1073/pnas.0807805105 |pmid=19020100 |pmc=2596218}}</ref>

==Type 1 rhodopsins==
All-''trans''-retinal is also an essential component of type I, or microbial, opsins such as ], ], and ]. In these molecules, light causes the all-''trans''-retinal to become 13-''cis'' retinal,<ref name=13CIS>De-liang Chen, Guang-yu Wang, Bing Xu and Kun-sheng Hu. ''All-trans to 13-''cis'' retinal isomerization in light-adapted bacteriorhodopsin at acidic pH.'' Journal of Photochemistry and Photobiology B:Biology. 2002 Apr; 66(3):188-94. {{doi|10.1016/S1011-1344(02)00245-2}}</ref> which then cycles back to all-''trans''-retinal in the dark state.


==History== ==History==
The American biochemist ] and others had outlined the visual cycle by 1958. For his work, Wald won a share of the 1967 ] with ] and ].<ref></ref> The American biochemist ] and others had outlined the visual cycle by 1958. For his work, Wald won a share of the 1967 ] with ] and ].<ref></ref>


==See also== ==See also==
*]
*]
*]
*] *]
*]
*]


==References== ==References==
{{reflist}} {{Reflist}}


==Further reading== ==Further reading==
{{refbegin}} {{Refbegin}}
*{{cite journal |last=Prado-Cabrero |first=Alfonso |last2=Scherzinger |first2=Daniel |last3=Avalos |first3=Javier |last4=Al-Babili |first4=Salim |year=2007 |title=Retinal Biosynthesis in Fungi: Characterization of the Carotenoid Oxygenase CarX from Fusarium fujikuroi |journal=Eukayotic Cell |volume=6 |issue=4 |pages=650–657 |publisher=American Society for Microbiology |doi=10.1128/EC.00392-06 |pmid=17293483 |pmc=1865656}} *{{cite journal |last=Fernald |first=Russell D. |year=2006 |title=Casting a Genetic Light on the Evolution of Eyes |journal=Science |volume=313 |issue=5795 |pages=1914–1918 |doi=10.1126/science.1127889 |pmid=17008522 |bibcode=2006Sci...313.1914F |s2cid=84439732}}
* {{cite journal |last=Kloer |first=Daniel P. |last2=Ruch |first2=Sandra |last3=Al-Babili |first3=Salim |last4=Beyer |first4=Peter |last5=Schulz |first5=Georg E. |year=2005 |title=The Structure of a Retinal-Forming Carotenoid Oxygenase |journal=Science |volume=308 |issue=5719 |pages=267–269 |publisher=AAAS |doi=10.1126/science.1108965 |pmid=15821095}} *{{cite journal |last1=Amora |first1=Tabitha L. |last2=Ramos |first2=Lavoisier S. |last3=Galan |first3=Jhenny F. |last4=Birge |first4=Robert R. |year=2008 |title=Spectral Tuning of Deep Red Cone Pigments |journal=Biochemistry |volume=47 |issue=16 |pages=4614–20 |pmid=18370404 |doi=10.1021/bi702069d |pmc=2492582}}
*{{cite journal |last=Schmidt |first=Holger |last2=Kurtzer |first2=Robert |last3=Eisenreich |first3=Wolfgang |last4=Schwab |first4=Wilfried |year=2006 |title=The Carotenase AtCCD1 from Arabidopsis thaliana Is a Dioxygenase |journal=Journal of Biological Chemistry |volume=281 |issue=15 |pages=9845–9851 |publisher=ASBMB |doi=10.1074/jbc.M511668200 |pmid=16459333}} *{{cite journal |last1=Barlow |first1=H.B. |last2=Levick |first2=W.R. |last3=Yoon |first3=M. |year=1971 |title=Responses to single quanta of light in retinal ganglion cells of the cat |journal=Vision Research |volume=11 |issue=Supplement 3 |pages=87–101 |doi=10.1016/0042-6989(71)90033-2 |pmid=5293890}}
*{{cite journal |last=Wang |first=Tao |last2=Jiao |first2=Yuchen |last3=Montell |first3=Craig |year=2007 |title=Dissection of the pathway required for generation of vitamin A and for Drosophila phototransduction |journal=Journal of Cell Biology |volume=177 |issue=2 |pages=305–316 |publisher=Rockefeller University Press |doi=10.1083/jcb.200610081 |pmid=17452532 |pmc=2064138}} *{{cite journal |last1=Baylor |first1=D A |last2=Lamb |first2=T D |last3=Yau |first3=K W |year=1979 |title=Responses of retinal rods to single photons |journal=Journal of Physiology |volume=288 |pages=613–634 |pmid=112243 |doi=10.1113/jphysiol.1979.sp012716 |pmc=1281447 }}
*{{cite journal |last1=Fan |first1=Jie |last2=Woodruff |first2=Michael L |last3=Cilluffo |first3=Marianne C |last4=Crouch |first4=Rosalie K |last5=Fain |first5=Gordon L |year=2005 |title=Opsin activation of transduction in the rods of dark-reared Rpe65 knockout mice |journal=Journal of Physiology |volume=568 |issue=1 |pages=83–95 |doi=10.1113/jphysiol.2005.091942 |pmid=15994181 |pmc=1474752}}
*{{cite web |url=http://nobelprize.org/nobel_prizes/medicine/laureates/1967/wald-lecture.pdf |title=Nobel Lecture: The Molecular Basis of Visual Excitation |accessdate=2009-02-23 |last=Wald |first=George |authorlink=George Wald |year=1967}}
*{{cite journal |last=Fernald |first=Russell D. |year=2006 |title=Casting a Genetic Light on the Evolution of Eyes |journal=Science |volume=313 |issue=5795 |pages=1914–1918 |publisher=AAAS |doi=10.1126/science.1127889 |pmid=17008522 |bibcode=2006Sci...313.1914F}} *{{cite journal |last1=Hecht |first1=Selig |last2=Shlaer |first2=Simon |last3=Pirenne |first3=Maurice Henri |year=1942 |journal=Journal of General Physiology |volume=25 |issue=6 |pages=819–840 |doi=10.1085/jgp.25.6.819 |pmid=19873316 |pmc=2142545 |title=Energy, Quanta, and Vision}}
*{{cite journal |last1=Kawaguchi |first1=Riki |last2=Yu |first2=Jiamei |last3=Honda |first3=Jane |last4=Hu |first4=Jane |last5=Whitelegge |first5=Julian |last6=Ping |first6=Peipei |last7=Wiita |first7=Patrick |last8=Bok |first8=Dean |last9=Sun |first9=Hui |year=2007 |title=A Membrane Receptor for Retinol Binding Protein Mediates Cellular Uptake of Vitamin A |journal=Science |volume=315 |issue=5813 |pages=820–825 |doi=10.1126/science.1136244 |pmid=17255476 |bibcode=2007Sci...315..820K |s2cid=25258551|doi-access=free }}
*{{cite book |editor-last=Briggs |editor-first=Winslow R. |editor2-last=Spudich |editor2-first=John L. |title=Handbook of Photosensory Receptors |year=2005 |publisher=Wiley |isbn=978-3527310197}}
*{{cite journal |last=Baylor |first=D A |last2=Lamb |first2=T D |last3=Yau |first3=K W |year=1979 |title=Responses of retinal rods to single photons |journal=Journal of Physiology |volume=288 |issue= |pages=613–634 |publisher=Physiological Society |pmid=112243 |doi= |pmc=1281447}} *{{cite journal |last1=Kloer |first1=Daniel P. |last2=Ruch |first2=Sandra |last3=Al-Babili |first3=Salim |last4=Beyer |first4=Peter |last5=Schulz |first5=Georg E. |year=2005 |title=The Structure of a Retinal-Forming Carotenoid Oxygenase |journal=Science |volume=308 |issue=5719 |pages=267–269 |doi=10.1126/science.1108965 |pmid=15821095 |bibcode=2005Sci...308..267K |s2cid=6318853 }}
*{{cite journal |last=Hecht |first=Selig |last2=Shlaer |first2=Simon |last3=Pirenne |first3=Maurice Henri |year=1942 |title=Energy, Quanta, and Vision |journal=Journal of General Physiology |volume=25 |issue= 6|pages=819–840 |publisher=Rockefeller University Press |url=http://jgp.rupress.org/cgi/content/abstract/25/6/819 |accessdate=2008-03-05 |doi=10.1085/jgp.25.6.819 |pmid=19873316 |pmc=2142545}} *{{cite journal |last1=Luo |first1=Dong-Gen |last2=Xue |first2=Tian |last3=Yau |first3=King-Wai |year=2008 |title=How vision begins: An odyssey |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=29 |pages=9855–9862 |doi=10.1073/pnas.0708405105 |pmid=18632568 |pmc=2481352 |bibcode=2008PNAS..105.9855L|doi-access=free }} Good historical review.
*{{cite journal |last=Barlow |first=H.B. |last2=Levick |first2=W.R. |last3=Yoon |first3=M. |year=1971 |title=Responses to single quanta of light in retinal ganglion cells of the cat |journal=Vision Research |volume=11 |issue=Supplement 3 |pages=87–101 |publisher=Elsevier |doi=10.1016/0042-6989(71)90033-2 |pmid=5293890}} *{{cite journal |last1=Prado-Cabrero |first1=Alfonso |last2=Scherzinger |first2=Daniel |last3=Avalos |first3=Javier |last4=Al-Babili |first4=Salim |year=2007 |title=Retinal Biosynthesis in Fungi: Characterization of the Carotenoid Oxygenase CarX from Fusarium fujikuroi |journal=] |volume=6 |issue=4 |pages=650–657 |doi=10.1128/EC.00392-06 |pmid=17293483 |pmc=1865656}}
*{{cite journal |last1=Racker |first1=Efraim |last2=Stoeckenius |first2=Walther |year=1974 |title=Reconstitution of Purple Membrane Vesicles Catalyzing Light-driven Proton Uptake and Adenosine Triphosphate Formation |journal=Journal of Biological Chemistry |volume=249 |issue=2 |pages=662–663 |doi=10.1016/S0021-9258(19)43080-9 |pmid=4272126 |doi-access=free}}
*{{cite journal |last=Venter |first=J. Craig |last2=et al. |authorlink=Craig Venter |year=2004 |title=Environmental Genome Shotgun Sequencing of the Sargasso Sea |journal=Science |volume=304 |issue=5667 |pages=66–74 |publisher=AAAS |doi=10.1126/science.1093857 |pmid=15001713 |first2=K |last3=Heidelberg |first3=JF |last4=Halpern |first4=AL |last5=Rusch |first5=D |last6=Eisen |first6=JA |last7=Wu |first7=D |last8=Paulsen |first8=I |last9=Nelson |first9=KE |bibcode=2004Sci...304...66V}} The oceans are full of type 1 rhodopsin.
*{{cite journal |last=Waschuk |first=Stephen A. |last2=Bezerra |first2=Arandi G. |last3=Shi |first3=Lichi |last4=Brown |first4=Leonid S. |year=2005 |title=Leptosphaeria rhodopsin: Bacteriorhodopsin-like proton pump from a eukaryote |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=19 |pages=6879–6883 |publisher= |doi=10.1073/pnas.0409659102 |pmid=15860584 |pmc=1100770}} *{{cite journal |last1=Sadekar |first1=Sumedha |last2=Raymond |first2=Jason|author3-link=Robert E. Blankenship |last3=Blankenship |first3=Robert E. |year=2006 |title=Conservation of Distantly Related Membrane Proteins: Photosynthetic Reaction Centers Share a Common Structural Core |journal=Molecular Biology and Evolution |volume=23 |issue=11 |pages=2001–2007 |doi=10.1093/molbev/msl079 |pmid=16887904 |doi-access=}}
*{{cite journal |last=Su |first=Chih-Ying |last2=Luo |first2=Dong-Gen |last3=Terakita |first3=Akihisa |last4=Shichida |first4=Yoshinori |last5=Liao |first5=Hsi-Wen |last6=Kazmi |first6=Manija A. |last7=Sakmar |first7=Thomas P. |last8=Yau |first8=King-Wai |year=2006 |title=Parietal-Eye Phototransduction Components and Their Potential Evolutionary Implications |journal=Science |volume=311 |issue=5767 |pages=1617–1621 |publisher=AAAS |doi=10.1126/science.1123802 |pmid=16543463}} *{{cite journal |last1=Salom |first1=David |last2=Lodowski |first2=David T. |last3=Stenkamp |first3=Ronald E. |last4=Le Trong |first4=Isolde |last5=Golczak |first5=Marcin |last6=Jastrzebska |first6=Beata |last7=Harris |first7=Tim |last8=Ballesteros |first8=Juan A. |last9=Palczewski |first9=Krzysztof |year=2006 |title=Crystal structure of a photoactivated deprotonated intermediate of rhodopsin |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=44 |pages=16123–16128 |doi=10.1073/pnas.0608022103 |pmid=17060607 |pmc=1637547 |bibcode=2006PNAS..10316123S|doi-access=free }}
*{{cite journal |last=Luo |first=Dong-Gen |last2=Xue |first2=Tian |last3=Yau |first3=King-Wai |year=2008 |title=How vision begins: An odyssey |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=29 |pages=9855–9862 |publisher= |doi=10.1073/pnas.0708405105 |pmid=18632568 |pmc=2481352}} Good historical review. *{{cite journal |last1=Schäfer |first1=Günter |last2=Engelhard |first2=Martin |last3=Müller |first3=Volker |year=1999 |title=Bioenergetics of the Archaea |journal=Microbiology and Molecular Biology Reviews |volume=63 |issue=3 |pages=570–620 |pmid=10477309 |doi=10.1128/MMBR.63.3.570-620.1999 |pmc=103747}}
*{{cite journal |last=Schäfer |first=Günter |last2=Engelhard |first2=Martin |last3=Müller |first3=Volker |year=1999 |title=Bioenergetics of the Archaea |journal=Microbiology and Molecular Biology Reviews |volume=63 |issue=3 |pages=570–620 |publisher=American Society for Microbiology |pmid=10477309 |doi= |pmc=103747}} *{{cite journal |last1=Schmidt |first1=Holger |last2=Kurtzer |first2=Robert |last3=Eisenreich |first3=Wolfgang |last4=Schwab |first4=Wilfried |year=2006 |title=The Carotenase AtCCD1 from Arabidopsis thaliana Is a Dioxygenase |journal=Journal of Biological Chemistry |volume=281 |issue=15 |pages=9845–9851 |doi=10.1074/jbc.M511668200 |pmid=16459333 |doi-access=free}}
*{{cite journal |last=Fan |first=Jie |last2=Woodruff |first2=Michael L |last3=Cilluffo |first3=Marianne C |last4=Crouch |first4=Rosalie K |last5=Fain |first5=Gordon L |last6= |first6= |last7= |first7= |last8= |first8= |last9= |first9= |year=2005 |title=Opsin activation of transduction in the rods of dark-reared Rpe65 knockout mice |journal=Journal of Physiology |volume=568 |issue=1 |pages=83–95 |publisher=Physiological Society |doi=10.1113/jphysiol.2005.091942 |pmid=15994181 |pmc=1474752}} *{{cite journal |last1=Send |first1=Robert |last2=Sundholm |first2=Dage |year=2007 |title=Stairway to the conical intersection: A computational study of retinal isomerization |journal=Journal of Physical Chemistry A |volume=111 |issue=36 |pages=8766–8773 |doi=10.1021/jp073908l |pmid=17713894 |bibcode=2007JPCA..111.8766S}}
*{{cite journal |last=Sadekar |first=Sumedha |last2=Raymond |first2=Jason |last3=Blankenship |first3=Robert E. |year=2006 |title=Conservation of Distantly Related Membrane Proteins: Photosynthetic Reaction Centers Share a Common Structural Core |journal=Molecular Biology and Evolution |volume=23 |issue=11 |pages=2001–2007 |publisher=Oxford University Press |doi=10.1093/molbev/msl079 |pmid=16887904}} *{{cite journal |last1=Su |first1=Chih-Ying |last2=Luo |first2=Dong-Gen |last3=Terakita |first3=Akihisa |last4=Shichida |first4=Yoshinori |last5=Liao |first5=Hsi-Wen |last6=Kazmi |first6=Manija A. |last7=Sakmar |first7=Thomas P. |last8=Yau |first8=King-Wai |year=2006 |title=Parietal-Eye Phototransduction Components and Their Potential Evolutionary Implications |journal=Science |volume=311 |issue=5767 |pages=1617–1621 |doi=10.1126/science.1123802 |pmid=16543463 |bibcode=2006Sci...311.1617S |s2cid=28604455 }}
*{{cite journal |last1=Venter |first1=J. Craig |last2=Remington |author-link=Craig Venter |year=2004 |title=Environmental Genome Shotgun Sequencing of the Sargasso Sea |journal=Science |volume=304 |issue=5667 |pages=66–74 |doi=10.1126/science.1093857 |pmid=15001713 |first2=K |last3=Heidelberg |first3=JF |last4=Halpern |first4=AL |last5=Rusch |first5=D |last6=Eisen |first6=JA |last7=Wu |first7=D |last8=Paulsen |first8=I |last9=Nelson |first9=KE |last10=Nelson |first10=W |last11=Fouts |first11=D. E. |last12=Levy |first12=S |last13=Knap |first13=A. H. |last14=Lomas |first14=M. W. |last15=Nealson |first15=K |last16=White |first16=O |last17=Peterson |first17=J |last18=Hoffman |first18=J |last19=Parsons |first19=R |last20=Baden-Tillson |first20=H |last21=Pfannkoch |first21=C |last22=Rogers |first22=Y. H. |last23=Smith |first23=H. O. |bibcode=2004Sci...304...66V |display-authors=8 |citeseerx=10.1.1.124.1840 |s2cid=1454587}} The oceans are full of type 1 rhodopsin.
*{{cite journal |last=Yokoyama |first=Shozo |last2=Radlwimmer |first2=F. Bernhard |year=2001 |title=The Molecular Genetics and Evolution of Red and Green Color Vision in Vertebrates |journal=Genetics |volume=158 |issue=4 |pages=1697–1710 |publisher=Genetics Society of America |pmid=11545071 |doi= |pmc=1461741}}
*{{cite journal |last=Racker |first=Efraim |last2=Stoeckenius |first2=Walther |year=1974 |title=Reconstitution of Purple Membrane Vesicles Catalyzing Light-driven Proton Uptake and Adenosine Triphosphate Formation |journal=Journal of Biological Chemistry |volume=249 |issue=2 |pages=662–663 |publisher=ASBMB |pmid=4272126 |doi=}} *{{cite journal |last1=Wang |first1=Tao |last2=Jiao |first2=Yuchen |last3=Montell |first3=Craig |year=2007 |title=Dissection of the pathway required for generation of vitamin A and for Drosophila phototransduction |journal=Journal of Cell Biology |volume=177 |issue=2 |pages=305–316 |doi=10.1083/jcb.200610081 |pmid=17452532 |pmc=2064138}}
*{{cite journal |last=Kawaguchi |first=Riki |last2=Yu |first2=Jiamei |last3=Honda |first3=Jane |last4=Hu |first4=Jane |last5=Whitelegge |first5=Julian |last6=Ping |first6=Peipei |last7=Wiita |first7=Patrick |last8=Bok |first8=Dean |last9=Sun |first9=Hui |year=2007 |title=A Membrane Receptor for Retinol Binding Protein Mediates Cellular Uptake of Vitamin A |journal=Science |volume=315 |issue=5813 |pages=820–825 |publisher=AAAS |doi=10.1126/science.1136244 |pmid=17255476}} *{{cite journal |last1=Waschuk |first1=Stephen A. |last2=Bezerra |first2=Arandi G. |last3=Shi |first3=Lichi |last4=Brown |first4=Leonid S. |year=2005 |title=Leptosphaeria rhodopsin: Bacteriorhodopsin-like proton pump from a eukaryote |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=19 |pages=6879–6883 |doi=10.1073/pnas.0409659102 |pmid=15860584 |pmc=1100770 |bibcode=2005PNAS..102.6879W|doi-access=free }}
*{{cite journal |last=Amora |first=Tabitha L. |last2=Ramos |first2=Lavoisier S. |last3=Galan |first3=Jhenny F. |last4=Birge |first4=Robert R. |year=2008 |title=Spectral Tuning of Deep Red Cone Pigments |journal=NIH Public Access Author Manuscript |volume= 47|issue= 16|pages= 4614–20|publisher= |pmid=18370404 |doi=10.1021/bi702069d |pmc=2492582}} *{{cite journal |last1=Yokoyama |first1=Shozo |last2=Radlwimmer |first2=F. Bernhard |year=2001 |title=The molecular genetics and evolution of red and green color vision in vertebrates |journal=Genetics |volume=158 |issue=4 |pages=1697–1710 |doi=10.1093/genetics/158.4.1697 |pmid=11545071 |pmc=1461741}}
*{{cite book |editor-last=Briggs |editor-first=Winslow R. |editor2-last=Spudich |editor2-first=John L. |title=Handbook of Photosensory Receptors |year=2005 |publisher=Wiley |isbn=978-3-527-31019-7}}
*{{cite journal |last=Send |first=Robert |last2=Sundholm |first2=Dage |year=2007 |title=Stairway to the conical intersection: A computational study of retinal isomerization |journal=Journal of Physical Chemistry A |volume=111 |issue=36 |pages=8766–8773 |publisher=American Chemical Society |doi=10.1021/jp073908l |pmid=17713894}}
*{{cite web |url=https://www.nobelprize.org/uploads/2018/06/wald-lecture.pdf |title=Nobel Lecture: The Molecular Basis of Visual Excitation |access-date=2009-02-23 |last=Wald |first=George |author-link=George Wald |year=1967}}
*{{cite journal |last=Salom |first=David |last2=Lodowski |first2=David T. |last3=Stenkamp |first3=Ronald E. |last4=Le Trong |first4=Isolde |last5=Golczak |first5=Marcin |last6=Jastrzebska |first6=Beata |last7=Harris |first7=Tim |last8=Ballesteros |first8=Juan A. |last9=Palczewski |first9=Krzysztof |year=2006 |title=Crystal structure of a photoactivated deprotonated intermediate of rhodopsin |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=44 |pages=16123–16128 |publisher= |doi=10.1073/pnas.0608022103 |pmid=17060607 |pmc=1637547}}
{{refend}} {{Refend}}


==External links== ==External links==
* - National Health Museum * - National Health Museum
* *
* *
* *, Imperial College v-chemlib


{{Carotenoids}} {{Carotenoids}}
{{Authority control}}


] ]
]
]
]
] ]
]
]
]
]
]


]
]
] ]
]
]
]
]