Implications of torsional potential of retinal isomers for visual excitation.

Abstract

BECAUSE 11-cis retinal is the chromophore of the visual pigment in vertebrate rods, and its isomerization to the all-trans form (Ia) is known to occur during visual excitation1–4, the properties of the retinal isomers are of considerable interest. Although it has long been assumed that non-bonded repulsions in 11-cis retinal distort the polyene chain, the details of the ground state geometry have not been determined, nor has the experimental spectrum been correlated unequivocally with the excited states. In this communication, we present a theoretical ground state potential function with a form which may help to explain some of the unusual spectral characteristics of the retinal isomers when in solution or incorporated into the native visual pigment1–4.