Crystallographic Analysis of Primary Visual Photochemistry

A curved retinal: Difference electron-density data between the photoreceptor protein rhodopsin and its primary photoreaction intermediate bathorhodopsin have provided a crystallographic model for the cis–trans isomerization of the chromophore retinal therein during the primary process in dim-light vision (see picture; the curved polyene structure of retinal in bathorhodopsin is shown in red, while that in rhodopsin is colored green).