11cisretinaldehyde

11-cisretinaldehyde, also written 11-cis-retinaldehyde, is the aldehyde form of the 11-cis isomer of retinal, the vitamin A metabolite. The molecule is a long-chain polyene aldehyde with a cis configuration at carbon 11. In vertebrate vision, 11-cis-retinaldehyde acts as the chromophore of opsin proteins. In rhodopsin, it forms a Schiff base with a lysine residue, creating the light-absorbing pigment in rod cells. When photons are absorbed, 11-cis-retinaldehyde is isomerized to all-trans-retinal, triggering the phototransduction cascade and leading to a neural signal.

The all-trans-retinal is released from opsin and reduced to all-trans-retinol, which travels to the retinal pigment epithelium (RPE). There it is converted back through the visual cycle: all-trans-retinol is oxidized to all-trans-retinyl esters, isomerized and hydrolyzed by the isomerohydrolase RPE65 to 11-cis-retinol, and finally oxidized to 11-cis-retinaldehyde. The regenerated chromophore is then transported back to photoreceptors and reattached to opsin to reform rhodopsin, restoring sensitivity to light.

11-cis-retinaldehyde is derived from dietary vitamin A and is maintained by retinoid-binding proteins that shuttle it between tissues. Disruptions in the retinoid cycle, including defects in RPE65, can impair regeneration of rhodopsin and contribute to night blindness and other retinal dystrophies.