Chemical Properties
Yellow Powder
Definition
ChEBI: A retinal in which all four exocyclic double bonds have E- (trans-) geometry.
General Description
All trans-Retinal is one of the major derivatives of vitamin A group. A variety of food serves as a source of vitamin A. It is predominant in liver and among the brightly colored vegetables.
Biological Activity
all-trans retinal, also known as vitamin a aldehyde or retinaldehyde, is one of the many forms of vitamin a and also the oxidation product of all-trans retinol [1]. all-trans retinal are associated with one of the two isoforms of cellular retinol-binding proteins (crbp-i and crbp-ii) with kd values of 50 and 90 nm, respectively [1].crbp-i and crbp-ii were the first intracellular retinoid-binding proteins. both proteins display a similar binding affinity towards retinal. they play important roles in retinoid biology and regulation of the metabolism of retinol and retinal. crbp-i is used to regulate vitamin a storage and synthesis of retinoic acid. and crbp-ii has a role in the initial processing of retinol from food [1].all-trans retinal is one form of vitamin a. all-trans retinal, the initial substrate of retinoid cycle, is a chemically reactive aldehyde that can form toxic conjugates with proteins and lipids, leading to degeneration of the retina [2].
Biochem/physiol Actions
All-trans retinal is converted to retinoic acid in vivo by the action of retinal dehydrogenase. Retinoic acid is a ligand for both the retinoic acid receptor (RAR) and the retinoid X receptor (RXR) that act as transcription factors to regulate the growth and differentiation of normal and malignant cells. Retinal isomers are also chromophores that bind to opsins, a family of G-protein-linked transmembrane proteins, to form photosensitive receptors in visual and nonvisual systems. All-trans retinal is a potent photosensitizer.
Purification Methods
The aldehyde is separated from retinol by column chromatography on water-deactivated alumina. Elute with 1-2% acetone in hexane, or on TLC plates of silica gel G and using the same eluting solvent. It crystallises from pet ether or n-hexane as yellow-orange crystals, and the UV in hexane has max at 373nm (A1cm 1% 1,548) and 368nm ( 48,000). It is an irritant and is light sensitive. Store it in sealed ampoules under N2. The semicarbazone forms yellow crystals from CHCl3/Et2O or EtOH, m 199-201o(dec). The 9-cis-isomer [514-85-2] and the 13-cis-isomer [472-86-6] [max at 375nm ( 1,250) in EtOH] are also available commercially. [Beilstein 7 III 1742.]
References
[1]. noy n. retinoid-binding proteins: mediators of retinoid action. biochem j. 2000 jun 15;348 pt 3:481-95.
[2]. kiser pd, golczak m, maeda a, et al. key enzymes of the retinoid (visual) cycle in vertebrate retina. biochim biophys acta. 2012 jan;1821(1):137-51.
