Coupling of charge stabilization, torsion and bond alternation in light-induced reactions of visual pigments

Abstract

The effect of external charges on the potential surfaces of protonated Schiff bases of retinal is reexamined. It is found that coupling of charge stabilization, torsion and bond alternation may account for the occurrence of intermediates in reactions of visual and purple membrane pigments. The calculations indicate that the light energy may be used not only for cis- trans isomerization about double bonds but also for trapping charge stabilized intermediates. This suggests the intriguing possibility that prelumirhodopsin might be still in the cis configuration.