Which retinal structure converts All-trans-retinol into 11-cis-retinal and plays a key role in phototransduction?

The retinal structure responsible for converting All-trans-retinol into 11-cis-retinal is the retinal pigment epithelium (RPE). This conversion is a crucial step in the visual cycle, which is essential for phototransduction—the process by which light is converted into electrical signals in the retina.

In this process, when photoreceptor cells (rods and cones) absorb light, the visual pigment rhodopsin undergoes a conformational change that results in the conversion of 11-cis-retinal to all-trans-retinal. To regenerate the visual pigment and allow for continued phototransduction, all-trans-retinal needs to be converted back to 11-cis-retinal. This regeneration occurs in the RPE, where enzymes, specifically isomerohydrolases, facilitate this conversion. Once 11-cis-retinal is formed, it can recombine with opsin in the photoreceptors, restoring their ability to detect light.

The roles of the other options are not centered on this specific conversion process. Photoreceptor outer segments contain the photopigments but do not perform the conversion of retinoids. The inner retina involves various neurons but does not participate in the conversion of retinoids either.