What is the inactivated form of the photoreceptor chromophore?

The inactivated form of the photoreceptor chromophore is 11-cis-retinal. In the context of phototransduction, when light photons are absorbed by the photoreceptive molecules in the retina, specifically by the opsins found in rod and cone cells, 11-cis-retinal undergoes isomerization to form all-trans-retinal. This conversion triggers a biochemical cascade that leads to the hyperpolarization of the photoreceptor cell, ultimately resulting in the perception of light.

11-cis-retinal is crucial for the visual cycle as it is the specific form of retinal that can bind to opsins, enabling the formation of the functional visual pigment rhodopsin in rods and photopsins in cones. When light is not present, 11-cis-retinal remains in its inactive state, ready to participate in the visual cycle upon exposure to light, illustrating its role in maintaining the photoreceptors in an unexcited, or inactive, state. This preparation is vital for the visual process to occur effectively.

In contrast, all-trans-retinal is actually the product of the isomerization reaction and represents the activated form of the chromophore, which leads to a temporary state of inactivity in terms