Application of Artificial Pigments to Structure Determination and Study of Photoinduced Transformations of Retinal Proteins

The protonated Schiff bases of all-trans-retinal and its double bond isomers, 11-cis- and 13-cis-retinals, comprise the chromophores of bacteriorhodopsin, sensory rhodopsin, rhodopsin, and the Chlamydomonas photoreceptor pigment. Absorption of photons by these chromophores is directly responsible for the functioning of the various photopigments. Clarification of their extremely complex structures and mechanisms requires multidisciplinary collaboration. The study of synthetic retinal analogs and pigments reconstituted from analogs provides a powerful and indispensable tool for such clarification. This article summarizes the application of retinal analogs in the bioorganic, biophysical, and biochemical investigations of the various retinal pigments.