Editing Retinal (section)

==Vitamin A metabolism==

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>

For example:
{{block indent|[[beta-carotene]] + O<sub>2</sub> → 2 retinal,}}

catalyzed by a [[beta-carotene 15,15'-monooxygenase]]<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>

Just as carotenoids are the precursors of retinal, retinal is the precursor of the other forms of vitamin A.  Retinal is interconvertible with [[retinol]], the transport and storage form of vitamin A:
{{block indent|retinal + [[nicotinamide adenine dinucleotide phosphate|NADPH]] + H<sup>+</sup> {{eqm}} retinol + NADP<sup>+</sup>}}
{{block indent|retinol + [[nicotinamide adenine dinucleotide|NAD]]<sup>+</sup> {{eqm}} retinal + NADH + H<sup>+</sup>,}}

catalyzed by [[retinol dehydrogenase]]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 [[alcohol dehydrogenase]]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>

Retinol is called vitamin A [[Alcohol (chemistry)|alcohol]] or, more often, simply vitamin A. Retinal can also be oxidized to [[retinoic acid]]:
{{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 [[retinal dehydrogenase]]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 [[retinal oxidase]]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>

Retinoic acid, sometimes called vitamin A [[carboxylic acid|acid]], is an important signaling molecule and hormone in vertebrate animals.