Fig. 1.

Chromophore regeneration in vertebrate and invertebrate photoreceptors. (A) Simplified version of the vertebrate visual cycle by which 11-cis retinaldehyde (Ra) is regenerated after bleach. The enzymes Lrat and Rpe65 (in white) are critical components of this pathway, which reside in the RPE. (B) In invertebrate rhabdomeric photoreceptors, opsin protein binds both cis- and trans-retinaldehyde, allowing photoregeneration of bleached photopigment. Rol, retinol. Opsin protein is represented in cartoon form by seven transmembrane α-helices.