9-Cis-Retinal

CAS 514-85-2

One bend can change the pigment formed by a visual protein. Rhodopsin normally contains 11-cis-retinal, while opsin combined with 9-cis-retinal forms the related photosensitive pigment isorhodopsin. The two retinal isomers have the same molecular formula but different double-bond geometry. Research dating to Hubbard and Wald's 1952 experiments used these differences to investigate visual-pigment formation. Later work identified isorhodopsin in dark-housed mice lacking RPE65, under conditions that disrupted the normal visual pathway. These findings make 9-cis-retinal a valuable research chromophore; they do not establish an approved treatment for human blindness. Distinguishing the isomers requires more than a mass measurement. The compound shows how a small change in molecular shape can become a controlled experiment on a protein's response to light and pigment assembly.