Abstract
Recent studies of quantum chemical calculations on visual pigments are summerized.
It is generally accepted that the red-shift and the wide distribution of λmax's (wavelengths of absorption maximum) of visual pigments can be explained by the protonated Schiff-base binding of retinal with opsin and by the electrostatic interaction between retinal and a counter-ion on opsin. Experimental and theoretical evidences for this primary linkage and interaction are first presented and discussed.
Secondly, recent studies of the secondary in teractions between retinal and opsin are summarized. At present, the following three types of the secondary interactions are mainly investigated: (1) the interaction of retinal through itsβ-ionone ring; (2) the interaction through its 9-methyl group; (3) the interaction with the local electric field due to the microenvironment of chromophore.
Thirdly, as for the photochemical conversion of rhodopsin to bathorhodopsin, it is generally considered that retinal isomerizes from 11-cis to all-trans form. Concerning to the mechanism of this isomerization, the potential surfaces of the ground and excited states have recently been examined by several authors. Their models for the intermediates in photobleaching process are reviewed and discussed briefly.
