Illustrated Glossary of Organic Chemistry

Retinal (vitamin A aldehyde; retinaldehyde): IUPAC name (2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraenal. A conjugated aldehyde, derived from oxidation of retinol. In the retina, retinal combines with opsin to form rhodopsin (visual purple), necessary for vision.


Enzyme



Retinol
Retinal
Enzymatic oxidation of retinol in the liver gives retinal.


+

Enzyme


Retinal
  
Opsin   
Rhodopsin
Retinal (shown in red) combines with the primary amine side chain of a lysine residue in opsin (shown in blue) to give rhodopsin.