What is the main chromophore of photoreceptors?

The main chromophore of photoreceptors is 11-cis retinal. This molecule is a derivative of vitamin A and is crucial for the phototransduction process that occurs in the retina. In photoreceptors, particularly rods and cones, 11-cis retinal is bound to opsin proteins to form visual pigments, which are essential for capturing light.

When photons hit these visual pigments, 11-cis retinal undergoes a conformational change to all-trans retinal. This transformation triggers a biochemical cascade that eventually leads to the generation of an electrical signal that the brain interprets as visual information. Thus, 11-cis retinal is the specific form that is involved in the initial step of vision, making it a fundamental component of how photoreceptors function.

While retinal refers to all forms, including 11-cis and all-trans isomers, and vitamin A is the precursor for retinal, it is 11-cis retinal that directly participates in the visual cycle. Therefore, identifying 11-cis retinal as the main chromophore highlights its pivotal role in photoreception and visual signal transduction.