Theory of the Optical Property of Visual Pigment

Abstract

Under the assumption that retinal forms a protonated or unprotonated Schiff-base binding with opsin, the effect of the electrostatic interaction between retinal and opsin on the optical property of visual pigment is investigated, using the π-electronic states determined previously with a due account of both σ-π interaction and configuration interaction. It is shown that the wide distribution of the observed wavelengths of absorption maximum of visual pigments can reasonably be explained by both the protonated Schiff-base binding and the electrostatic interaction of retinal with opsin. Furthermore, the origin of the electrostatic interaction is shown to be ascribable to one counter ion such as COO - at the vicinity of the protonated Schiff-base binding.