What is the activated form of the photoreceptor chromophore in light?

The activated form of the photoreceptor chromophore in light is all-trans-retinal. This compound is produced when light photons are absorbed by the retinal, a vitamin A derivative that is bound to opsin proteins in photoreceptors (rods and cones) in the retina.

When a photon of light strikes the 11-cis-retinal, it causes a conformational change to the all-trans-retinal form. This change is critical in initiating the phototransduction cascade, which ultimately leads to the conversion of light signals into electrochemical signals that can be interpreted by the brain.

In the absence of light, the chromophore is in the 11-cis-retinal form. Once light hits it, the transition to all-trans-retinal is what activates the visual cycle and enables the perception of light. The role of opsin is to hold the chromophore in place and facilitate the changes that occur, but it is the all-trans-retinal that is the active form responsible for signal transduction in the photoreceptors.

Other forms listed, such as retinaldehyde or the protein opsin itself, are not in active roles in response to light. Retinaldehyde refers to a form of retinal that is