retinaldehydi

Retinaldehyde, commonly referred to as retinal, is the aldehyde form of vitamin A (retinol) and serves as a crucial chromophore in vertebrate vision. In the retina, 11-cis-retinaldehyde is covalently bound to opsin proteins to form the visual pigments of rods and cones, such as rhodopsin. This binding enables the pigments to absorb light and initiate the visual signal.

When photons are absorbed, 11-cis-retinaldehyde photoisomerizes to all-trans-retinaldehyde, triggering a conformational change in the opsin protein and starting the phototransduction cascade that converts light into neural signals. The all-trans-retinaldehyde is then released and reduced to all-trans-retinol, which is transported to the retinal pigment epithelium for processing.

In the visual cycle, all-trans-retinol is enzymatically converted back to 11-cis-retinaldehyde and reattached to opsin, regenerating the light-sensitive pigment. This recycling allows continuous vision under varying light conditions. Retinaldehyde is derived from dietary vitamin A and provitamin A carotenoids, and it exists in different isomeric forms depending on light exposure and enzymatic steps.

Chemically, retinaldehyde is an aldehyde with a reactive aldehyde group that participates in Schiff base formation with lysine residues on opsins, a key feature of its function as a chromophore. Deficiencies in vitamin A or defects in the visual cycle can impair rhodopsin regeneration, leading to impaired dark adaptation or night blindness if untreated.